1. No category

Correction of beam wander for a free-space quantum key
distribution system operating in urban environment
Alberto Carrasco-Casado, Natalia Denisenko, Veronica Fernandez
Spanish National Research Council (CSIC)
Institute of Physical and Information Technologies (ITEFI)
Serrano 144, 28006 Madrid, Spain
Abstract. Free-space quantum key distribution links in urban environment have demanding operating
needs, such as functioning in daylight and under atmospheric turbulence, which can dramatically impact
their performance. Both effects are usually mitigated with a careful design of the field of view of the
receiver. However, a trade-off is often required, since a narrow field of view improves background noise
rejection but it is linked to an increase in turbulence-related losses. In this paper, we present a high-speed
automatic tracking system to overcome these limitations. Both a reduction in the field-of-view to decrease
the background noise and the mitigation of the losses caused by atmospheric turbulence are addressed.
Two different designs are presented and discussed, along with technical considerations for the
experimental implementation. Finally, preliminary experimental results of beam wander correction are
used to estimate the potential improvement of both the quantum bit error rate and secret key rate of a
free space quantum key distribution system.
Keywords: quantum cryptography, quantum key distribution, automatic tracking, beam wander,
atmospheric turbulence, free-space optical communications.
Address all correspondence to: Alberto Carrasco-Casado, Spanish National Research Council (CSIC),
Institute of Physical and Information Technologies (ITEFI), Serrano 144, Madrid, Spain, 28006; Tel: +34
915618806 ext. 446; E-mail: [email protected]
1
Introduction
Quantum key distribution (QKD) [1], and quantum cryptography in general, has become a new
paradigm in data protection. The laws of quantum mechanics offer a theoretically-secure
alternative for data communications over conventional methods, since the presence of an
eavesdropper can be uniquely detected in the process of key sharing over an insecure channel.
Free-space QKD has been extensively aimed to satellite communications with the main
efforts concentrating in achieving long distances to proof its feasibility [2]. However, short
distance (inter-city range) free-space QKD links in urban areas may also offer some advantages
over optical fiber, such as flexibility of installation and portability. Unlike optical fiber-based
systems, free-space-based links can be easily transported to different locations if required. In
1
Photo-Thermal Transfer Function of Dielectric Mirrors for Precision Measurements
Stefan W. Ballmer1, ∗
arXiv:1411.3365v1 [physics.optics] 10 Nov 2014
1
Department of Physics, Syracuse University, NY 13244, USA
(Dated: November 14, 2014)
The photo-thermal transfer function from absorbed power incident on a dielectric mirror to the
effective mirror position is calculated using the coating design as input. The effect is found to
change in amplitude and sign for frequencies corresponding to diffusion length comparable to the
coating thickness. Transfer functions are calculated for the T i-doped Ta2 O5 : SiO2 coating used in
Advanced LIGO and for a crystalline Alx Ga1−x As coating. The shape of the transfer function at
high frequencies is shown to be a sensitive indicator of the effective absorption depth, providing
a potentially powerful tool to distinguish coating-internal absorption from surface contamination
related absorption. The sign change of the photo-thermal effect could also be useful to stabilize
radiation pressure-based opto-mechanical systems. High frequency corrections to the previously
published thermo-optic noise estimates are also provided. Finally, estimating the quality of the
thermo-optic noise cancellation occurring in fine-tuned Alx Ga1−x As coatings requires the detailed
heat flow analysis done in this paper.
I.
INTRODUCTION
The photo-thermal effect is the coupling from fluctuations in absorbed power incident on a mirror to the effective mirror position. It is important for a wide range
of applications involving varying amounts of power incident on a mirror. Examples range from a source of
noise coupling in gravitational-wave interferometers to
an important feed-back path in many types of micoelectromechanical systems. Additionally, the photothermal effect is closely related to the thermo-optic noise
in mirror coatings, which is one of the limiting noise
sources for upgrades to the gravitational-wave interferometers currently under construction (Advanced LIGO
[18], Advanced Virgo [1] and Kagra [23]). The importance of the effect for gravitational wave detectors has
driven a theoretical [3–6, 11, 13, 19, 20] and experimental
[8, 10, 16–18, 22] interest in understanding and improving
the fundamental thermal noise of optical elements.
The photo-thermal transfer function takes a simple
form at frequencies for which the diffusion length ddiff is
small compared to the transverse dimension of the beam
spot, but large compared to the coating thickness dcoat .
Both the thermal diffusion and the elasticity problem become one-dimensional, and the resulting mirror surface
displacement is the integral of the deposited heat (equation 1 below). In [6] Cerdonio et al. explored corrections to this simple picture that arise due to transverse
diffusion. Their result predicted a decrease in the photothermal response for frequencies corresponding to diffusion length comparable to the beam spot (equation 2 below). This result was later experimentally confirmed by
De Rosa et al. [10], measuring the coupling up to 200 Hz.
Both papers however assume that the diffusion length is
much bigger than the coating thickness.
The dielectric stack of the mirror coating affects both
∗
[email protected]
the heat diffusion at higher frequencies and the local coupling of temperature to the total reflected phase of the
coating, which is the quantity that determines the mirror
position read-out. The latter was discussed in detail in
[13] in the context of exploring thermo-optic noise. In
particular we found that, compared to substrate heating, heating of the first couple of dielectric layers has the
opposite effect on the mirror position read-out. This is
caused by the change in optical thickness of the dielectric
layers. However [13] did not discuss the implications for
the photo-thermal transfer function, which is explored in
this paper.
The rest of the paper is structured as follows: Section II revisits the previously published properties of the
photo-thermal effect. In section III the photo-thermal
transfer function is calculated taking into account the
coating structure. Section IV applies the result to both
the T i-doped Ta2 O5 : SiO2 coating used in Advanced
LIGO and for a crystalline Alx Ga1−x As coating. In section V the implications for thermo-optic noise are discussed.
II.
SUBSTRATE PHOTO-THERMAL
COUPLING
In the limit where the coating thickness dcoat is negligible compared to the diffusion length ddiff and transverse
diffusion is irrelevant, dcoat ddiff w, with w is the
Gaussian beam radius, the photo-thermal transfer function takes the form
Z ∞
j
¯ T dz = α
¯
.
(1)
4z = α
iωρC
0
p
Here ddiff = κ/(ρCω) is the diffusion length in the substrate, with κ, C and ρ the thermal conductivity, heat
capacity and density of the material. ω and j are the observation frequency and the absorbed surface intensity.
Finally, α
¯ = 2(1 + σ)α is the effective expansion coefficient under the mechanical constraint that the heated
Cross-calibration of the Transition Radiation Detector of AMS-02 for an Energy
Measurement of Cosmic-Ray Ions
A. Obermeier, M. Korsmeier for the AMS-02 collaboration
arXiv:1411.3329v1 [astro-ph.IM] 12 Nov 2014
I. Physikalisches Institut B, RWTH Aachen University, Aachen, Germany
Abstract
Since May 2011 the AMS-02 experiment is installed on the International Space Station and is observing cosmic
radiation. It consists of several state-of-the-art sub-detectors, which redundantly measure charge and energy of traversing
particles. Due to the long exposure time of AMS-02 of many years the measurement of momentum for protons and ions
is limited systematically by the spatial resolution and magnetic field strength of the silicon tracker. The maximum
detectable rigidity for protons is about 1.8 TV, for helium about 3.6 TV. We investigate the possibility to extend the
range of the energy measurement for heavy nuclei (Z ≥ 2) with the transition radiation detector (TRD). The response
function of the TRD shows a steep increase in signal from the level of ionization at a Lorentz factor γ of about 500
to γ ≈ 20000, where the transition radiation signal saturates. For heavy ions the signal fluctuations in the TRD are
sufficiently small to allow an energy measurement with the TRD beyond the limitations of the tracker. The energy
resolution of the TRD is determined and reaches a level of about 20% for boron (Z = 5). After adjusting the operational
parameters of the TRD a measurement of boron and carbon could be possible up to 5 TeV/nucleon.
Keywords: transition radiation, proportional tubes, space-borne detector, cosmic rays
PACS: 29.40.Cs, 98.70.Sa, 07.87.+v
1. Introduction
Transition radiation detectors (TRDs) have a long tradition in direct cosmic-ray measurements. They have been
utilized as threshold detectors already by e.g. Hartmann et
al. (1977) and Prince (1979), recently by HEAT (Barwick
et al., 1997), and now by the AMS-02 (Aguilar et al., 2013)
experiment. They have been used to measure the energy
of highly relativistic cosmic-ray nuclei in several other experiments: CRN (L’Heureux et al., 1990), TRACER (Ave
et al., 2011), and CREAM1 (Ahn et al., 2007).
The light weight per area and signal response at very
high energies make transition radiation detectors valuable
for the direct observation of cosmic radiation on balloonborne or space-based experiments. Transition radiation
(TR) is emitted as x-ray photons (Cherry, 1978) by particles with Lorentz factors γ above about 1000, when they
traverse boundaries of different dielectric constants. Above
the threshold the TR yield increases with Lorentz factor,
until it reaches saturation usually above γ ≈ 104 . The
exact onset of TR, the shape of the response curve, and
its saturation depend on the radiator materials and the
detector configuration. It is an advantage of TRDs that
they can be calibrated with light particles over the whole
Email address: [email protected] (A.
Obermeier)
1 Although the exposure for CREAM was not sufficient to actually
observe TR events.
Preprint submitted to Advances in Space Research
range of their response, see e.g. L’Heureux et al. (1990).
About 100 boundary transitions are needed on average for
a singly charged particle to emit one TR photon. In practice this means that a lot of boundaries are needed in a
TRD (realized with foam radiators) and that an energy
measurement is usually only possible for heavier nuclei
that produce more signal (the TR yield scales with Z 2 ).
For more information on TRDs see Wakely et al. (2004),
M¨
uller (2004), and references therein.
In this paper we investigate the possibility to use the
TRD of the AMS-02 experiment for energy measurements
of heavy cosmic-ray nuclei. First, the AMS-02 experiment
is described. Then the response curve of the transition
radiation detector is determined and the energy resolution
calculated.
2. The AMS-02 experiment
The AMS-02 experiment is a multi-purpose cosmic-ray
detector installed on the International Space Station (ISS)
since May 16th 2011. Its active detector elements consist
of a silicon tracker within a strong magnetic field, a timeof-flight detector (ToF), a ring imaging Cerenkov detector,
an electromagnetic calorimeter (ECAL), and a transition
radiation detector (TRD). A detailed description of the
detector is available by Aguilar et al. (2013) and references
therein. A schematic view of the detector is shown in
Figure 1.
November 14, 2014
Feasibility Study of φ (1020) Production at NICA/MPD
arXiv:1411.3516v1 [physics.ins-det] 13 Nov 2014
L. S. Yordanova and V. I. Kolesnikov
for the MPD Collaboration
Veksler and Baldin Laboratory of High Energy Physics,
Joint Institute for Nuclear Research,
141980 Dubna, Moscow region, Russia
e-mail: [email protected]
Abstract. The goal of this article is to give information about the new accelerator complex NICA at JINR, to provide overview
of the MultiPurpose Detector (MPD) and its subdetectors and to present the current results of the MPD performance for φ meson production. In our study we use √
the channel decay Φ → K + K − to detect the formation of the φ -meson. UrQMD event
generator is used and central events at s = 11 GeV are analyzed. The obtained peak from the invariant mass distribution is
fitted by a Breit-Wigner function. The calculated values of the parameters are consistent with the values given in literature.
This study shows that the measurement of φ -mesons is feasible at NICA/MPD.
Keywords: NICA/MPD, strange mesons, φ (1020) production
PACS: 14.40.Df, 13.25.Es, 12.38.Aw
1. INTRODUCTION
The Nuclotron-based Ion Collider fAcility (NICA) is a new accelerator complex being constructed at JINR, Dubna,
Russia (Fig. 1). The global scientific goal of the NICA/MPD project is to explore the phase diagram of strongly
interacting matter in the region of highly compressed baryonic matter. The study of hot and dense baryonic matter
provides relevant information on the in-medium properties of hadrons and nuclear matter equation of state; allows
a search for deconfinement and/or chiral symmetry restoration, phase transition, mixed phase and critical end-point,
possible strong P- and CP violation; gives information about the evolution of the Early Universe and the formation of
neutron stars [1].
NICA’s aim is to provide collisions of heavy ions over a wide range of atomic masses, from Au+Au collisions at
√
√
sNN = 11 GeV (for Au79+ ) and an average luminosity of L = 1027 cm−2 s−1 to proton-proton collisions with s pp
32
−2
−1
= 20 GeV and L ∼ 10 cm s . Two interaction points are foreseen at NICA which provide a possibility for two
detectors to operate simultaneously - MultiPurpose Detector (MPD) and Spin Physics Detector (SPD). This overview
is focused on the MPD detector.
The MPD experimental program includes simultaneous measurements of observables that are presumably sensitive
to high nuclear density effects and phase transitions.The goal to start energy scan as soon as the first beams are available
and the present constraints in resources and manpower lead to the MPD staging. In the first stage of the project (starting
in 2017) are considered - multiplicity and spectral characteristics of the identified hadrons including strange particles,
multi-strange baryons and antibaryons; event-by-event fluctuations in multiplicity, charges and transverse momentum;
collective flows (directed, elliptic and higher ones) for observed hadrons. In the second stage (starting in 2020) the
electromagnetic probes (photons and dileptons) will be measured. It is proposed that along with heavy ions NICA will
provide proton and light ion beams including the possibility to use polarized beams [2].
The software of the MPD project is responsible for the design, evaluation and calibration of the detector; the storage,
access, reconstruction and analysis of the data; and the support of a distributed computing infrastructure.The software
framework for the MPD experiment (MpdRoot) is based on the object-orientated framework FairRoot (developed at
GSI) and provides a powerful tool for detector performance studies, development of algorithms for reconstruction and
physics analysis of the data [3]. Extended set of event generators for heavy ion collisions is used (UrQMD, LAQGSM,
HSD).
arXiv:1411.3485v1 [physics.ins-det] 13 Nov 2014
Vertexing and Tracking Software at Belle II
Tobias Schlüter∗ for the Belle II Software Group
Ludwig-Maximilians-Universität
E-mail: [email protected]
Belle II is a B factory experiment aiming to start physics data taking in 2017. It is currently being
set up at the SuperKEKB accelerator at the KEK facility in Tsukuba (Japan), an asymmetric e+ e−
collider which aims to achieve an unprecedented instantaneous luminosity of 8 · 1035 Hz/cm2 .
This forty-fold increase over predecessor experiments is achieved by employing a novel nanobeam scheme. Originally developed for the now-defunct SuperB experiment, this scheme allows
a significant increase in luminosity at only modest increases of beam currents. Challenges for the
vertex detector result from increased data and background rates. At full luminosity, physics data
will be recorded at a rate of 30 kHz. The radiation-hard DEPFET-sensors of the innermost layer
of the vertex detector will be read out employing a novel data-reduction scheme using selective
detector read out based on online reconstruction of event data. Belle II uses a software framework
in which data handling is unified between various data processing modules. In this way, tasks can
be divided flexibly and the same software framework can be used for a diversity of tasks ranging
from the high-level trigger to final processing of plots for publications. Tracking and vertexing
modules are currently under development and we will discuss their features.
PACS: 29.40.Gx, 29.85.Ca, 29.85.-c
The 23rd International Workshop on Vertex Detectors
15-19 September 2014
Macha Lake, The Czech Republic
∗ This
research was supported by the DFG cluster of excellence ’Origin and Structure of the Universe’ and under
BMBF Contract 05H12WM8.
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Phase Control of Squeezed Vacuum States of Light in Gravitational Wave Detectors
K. L. Dooley,1, ∗ E. Schreiber,1 H. Vahlbruch,1 C. Affeldt,1 J. R. Leong,1 H. Wittel,1 and H. Grote1
arXiv:1411.3454v1 [physics.ins-det] 13 Nov 2014
1
Max-Planck-Institut f¨
ur Gravitationsphysik (Albert Einstein Institut) and
Leibniz Universit¨
at Hannover, Callinstr. 38, 30167 Hannover, Germany
(Dated: November 14, 2014)
Quantum noise will be the dominant noise source for the advanced laser interferometric gravitational wave detectors currently under construction. Squeezing-enhanced laser interferometers have
been recently demonstrated as a viable technique to reduce quantum noise. We propose two new
methods of generating an error signal for matching the longitudinal phase of squeezed vacuum states
of light to the phase of the laser interferometer output field. Both provide a superior signal to the
one used in previous demonstrations of squeezing applied to a gravitational-wave detector. We
demonstrate that the new signals are less sensitive to misalignments and higher order modes, and
result in an improved stability of the squeezing level. The new signals also offer the potential of
reducing the overall rms phase noise and optical losses, each of which would contribute to achieving
a higher level of squeezing. The new error signals are a pivotal development towards realizing the
goal of 6 dB and more of squeezing in advanced detectors and beyond.
I.
INTRODUCTION
The dominant broadband noise source for the advanced laser interferometric gravitational wave (GW) detectors will be quantum noise [1–3]. The classical method
for reducing quantum noise at shot-noise-limited frequencies is to increase the laser power. Higher laser power,
however, introduces many technical challenges arising
from laser light absorption and subsequent heating of
the optics. Another approach to reduce quantum noise
is to inject squeezed states of light into the interferometer’s anti-symmetric port, a technique which reduces
the measurement uncertainty in the readout signal [4].
Rapid advances in both squeezing technology and laser
interferometer development in the last decade resulted
in the first demonstrations of this quantum noise reduction technique on current interferometric GW detectors
in 2010 at GEO 600 [5] and in 2011 at LIGO Hanford [6].
GEO 600 is carrying out the first long-term study of
incorporating squeezed states of light in a GW detector.
Results include demonstration of a squeezing duty cycle
of 90% with mean detected squeezing of 2.0 dB during
an 11 month data collection period in 2012 [7]. Continued work since then has resulted in an increase of the
observed squeezing level up to a maximum of 3.7 dB to
date and a continued high duty cycle of 85% [8]. This
study has demonstrated the readiness of squeezed states
of light as a permanent application for increasing the
astrophysical reach of GW detectors. Projects such as
Advanced LIGO and Advanced Virgo are now making
plans to incorporate squeezing as an early instrumental
upgrade.
The limits to the level of non-classical noise reduction that can be achieved depend on the following four
variables: degree of generated squeezing, optical losses
(including beam alignment and mode-matching), phase
∗ Please
address correspondence to: [email protected]
squeezing
quadrature
measurement
quadrature
X2
E
X 2 = er
X1=e-r
X1
FIG. 1: Phasor diagram of a squeezed state (∆X1 ∆X2 ≥ 1).
The factor r describes the degree of squeezing and antisqueezing for a pure state and φ describes the mismatch in
angle between the squeezing and measurement quadratures.
For application in a GW detector, phase squeezing is injected
to the anti-symmetric port.
noise, and noises in the squeezing frequency band other
than shot noise. This paper focuses on new techniques
developed, implemented, and analyzed at GEO 600 which
serve to reduce phase noise.
Phase noise refers to any root-mean-square (rms) difference between the angle of the squeezing ellipse and
the angle of the measurement quadrature of the interferometer as depicted in Fig. 1. The degree of measurable
squeezing and anti-squeezing is reduced for an rms phase
noise of φ π as follows:
Vs0 = Vs cos2 φ + Va sin2 φ
Va0 = Va cos2 φ + Vs sin2 φ
(1)
(2)
where Vs and Va are the variances of the squeezed and
anti-squeezed states, respectively, before including the effect of phase noise.
Phase noise, also called ‘quadrature fluctuations’ or
‘squeezing angle jitter’, is one of the limits to quantum
arXiv:1411.3705v1 [hep-ph] 13 Nov 2014
JET : A Global Jet Finding Algorithm
Yang Bai,a Zhenyu Hanb and Ran Lua
a
a
Department of Physics, University of Wisconsin, Madison, WI 53706, USA
Institute for Theoretical Science, University of Oregon, Eugene, OR 97403, USA
Abstract
We introduce a new jet-finding algorithm for a hadron collider based on maximizing a
JET function for all possible combinations of particles in an event. This function prefers
a larger value of the jet transverse energy and a smaller value of the jet mass. The jet
shape is proved to be a circular cone in Cartesian coordinates with the geometric center
shifted from the jet momentum toward the central region. The jet cone size shrinks for
a more forward jet. We have implemented our JET algorithm with a reasonable running
time scaling as N n3 , where “N ” is the total number of particles and “n” ( N ) is the
number of particles in a fiducial region. Many features of our JET jets are similar to
anti-kt jets, including the reconstructed jet momentum and the “back-reaction” from soft
contamination. Nevertheless, when the jet parameters in the two algorithms are matched
using QCD jets, we find that the JET algorithm has a larger efficiency than anti-kt for
identifying objects with hard splittings such as a W -jet.
THÈSE
Pour obtenir le grade de
DOCTEUR DE L’UNIVERSITÉ DE GRENOBLE
Spécialité : Physique théorique
arXiv:1411.3465v1 [hep-ph] 13 Nov 2014
Arrêté ministériel : 7 août 2006
Présentée par
Béranger Dumont
Thèse dirigée par Sabine Kraml
préparée au sein LPSC Grenoble
et de l’école doctorale de physique
Higgs, supersymmetry and dark
matter after Run I of the LHC
Thèse soutenue publiquement le 24/09/2014,
devant le jury composé de :
Pr. Johann Collot
Professeur, LPSC Grenoble, Université de Grenoble, Président
Dr. Abdelhak Djouadi
Directeur de recherche CNRS, LPT Orsay, Université Paris-Sud XI, Rapporteur
Pr. Manuel Drees
Professor, Bethe Center for Theoretical Physics, Universität Bonn, Rapporteur
Dr. Geneviève Bélanger
Directeur de recherche CNRS, LAPTh, Université de Savoie, Examinatrice
Dr. Veronica Sanz
Lecturer, University of Sussex, Examinatrice
Dr. Cyril Hugonie
Maître de conférences, LUPM, Université Montpellier 2, Examinateur
Dr. Sabine Kraml
Directeur de recherche CNRS, LPSC Grenoble, Université de Grenoble, Directeur
de thèse
Contents
1 Introduction
1.1 A brief overview of the Standard Model . . . . . . . . .
1.2 The need for BSM physics . . . . . . . . . . . . . . . .
1.2.1 Theoretical problems: hierarchy and aesthetics .
1.2.2 Observational problems: dark matter and others
1.3 Supersymmetry . . . . . . . . . . . . . . . . . . . . . .
1.3.1 Supersymmetric Lagrangians . . . . . . . . . . .
1.3.2 The MSSM . . . . . . . . . . . . . . . . . . . .
1.4 Dark matter: the last gasp of WIMPs? . . . . . . . . .
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least a Higgs boson
Pre-LHC constraints on the Higgs boson . . . . . . . . . . . . . . . . .
Production and decay of the SM Higgs boson at the LHC . . . . . . . .
Discovery and measurements at the LHC . . . . . . . . . . . . . . . . .
Constraining new physics with the LHC Higgs results . . . . . . . . . .
The excitement about an excess in the diphoton channel in 2012 . . . .
2.5.1 Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.2 Experimental inputs and fitting procedure . . . . . . . . . . . .
2.5.3 Fits to reduced Higgs couplings . . . . . . . . . . . . . . . . . .
2.5.4 Application to two-Higgs-Doublet Models . . . . . . . . . . . . .
2.5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6 The status of Higgs couplings after Moriond 2013 . . . . . . . . . . . .
2.6.1 Methodology and combined signal strengths ellipses . . . . . . .
2.6.2 Fits to reduced Higgs couplings . . . . . . . . . . . . . . . . . .
2.6.3 Interplay with direct dark matter searches . . . . . . . . . . . .
2.6.4 Application to two-Higgs-Doublet Models . . . . . . . . . . . . .
2.6.5 Application to the Inert Doublet Model . . . . . . . . . . . . . .
2.6.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7 A Bayesian view of the Higgs sector with higher dimensional operators
2.7.1 Electroweak higher-dimension operators . . . . . . . . . . . . .
2.7.2 Data treatment . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7.3 On weak bosons tensorial couplings . . . . . . . . . . . . . . . .
2.7.4 Deviations caused by new physics . . . . . . . . . . . . . . . . .
2.7.5 Bayesian setup and low-Λ scenario . . . . . . . . . . . . . . . .
2.7.6 Inference on HDOs . . . . . . . . . . . . . . . . . . . . . . . . .
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APS/123-QED
Some of semileptonic and nonleptonic decays of Bc meson in a Bethe-Salpeter
relativistic quark model
Chao-Hsi Chang∗
CCAST (World Laboratory), P.O.Box 8730, Beijing 100190, China.
State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,
Chinese Academy of Sciences, Beijing 100190, China.
Hui-Feng Fu†
arXiv:1411.3428v1 [hep-ph] 13 Nov 2014
Department of Physics, Tsinghua University, Beijing 100084, China.
Guo-Li Wang‡
Department of Physics, Harbin Institute of Technology, Harbin 150001, China.
Jin-Mei Zhang§
Xiamen Institute of Standardization, Xiamen 361004, China.
(Dated: November 14, 2014)
The semileptonic decays Bc+ → P (V ) + ℓ+ + ν¯ℓ and the nonleptonic decays Bc+ → P (V ) + L,
where P or V denotes a S-wave charmonium or a S-wave (¯bs) bound state and L denotes a light
meson, are studied under the framework of improved instantaneous Bethe-Salpeter (BS) equation
and the Mandelstam formula. We present the numerical results about the width and branching
ratio of each decay mode in tables. In order to compare with the others conveniently, the results
obtained by other approaches are also presented in the relevant tables. Based on the fact that the
+
BR(Bc
→ψ(2S)π + )
ratio
= 0.24 estimated in terms of the present framework is in agreement with the
+
+
BR(Bc →J/ψπ )
BR(B + →ψ(2S)π + )
c
= 0.250 ± 0.068(stat) ± 0.014(syst) ± 0.006(B) quite well, one
LHCb observation
+
BR(Bc
→J/ψπ + )
may see that the approach adopted here to the decays is really improved in comparison with the
early one.
PACS numbers: 13.20.He, 13.25.Ft, 13.25.Hw, 14.40.Lb, 14.40.Nd
Bc meson carries two heavy flavor quantum numbers
explicitly, and it decays only via weak interactions, although the strong and electromagnetic interactions can
affect the decays. As consequences, Bc meson has a comparatively long lifetime and very rich weak decay channels with sizable branching ratios. Moreover, as an explicit double heavy flavor meson, its production cross section can be calculated by perturbative QCD quite reliably and the conclusion can be drawn that only via strong
interaction and at hadronic high energy collisions the meson can be produced so numerously that one can observe
it experimentally [1–3]. Therefore, the meson is specially
interesting in studying its production and decays.
The first successful observation of Bc was achieved
through the semileptonic decay channel Bc → J/ψ +ℓ+ +
ν¯ℓ by CDF collaboration in 1998 from Run-I at Tevatron.
They obtained the mass of Bc : mBc = 6.40 ± 0.39 ± 0.13
+0.18
±0.03 ps [4]. Later
GeV and the lifetime: τBc = 0.46−0.16
on CDF collaboration gave a more precise mass mBc =
6275.6 ± 2.9(stat)±5(syst) MeV/c2 obtained through the
∗ Electronic
address:
address:
‡ Electronic address:
§ Electronic address:
† Electronic
[email protected]
[email protected]
gl˙[email protected]
[email protected]
exclusive non-leptonic decay Bc → J/ψπ + [5], and upgraded their results [6]. D0 collaboration at Tevatron has
also carried out the observations and confirmed CDF results [7]. Now LHCb has reported several observations on
Bc decays [8], and it is expected that in the near future
the Bc data will be largely enhanced.
In literatures, there has been many works studying various Bc decays [9–24] under different approaches. Among
the approaches in the market, the one used in Ref. [9] is
based on the instantaneous Bethe-Salpeter (BS) equation
[25] (also called Salpeter equation [26])1 with a QCDinspired kernel (interaction) for heavy quarks and the
Mandelstam formula [27] for the relevant hadron matrix
elements. This approach has a firm foundation and may
well take into account of the relativistic “recoil effects”
in the decays because the BS equation and the Mandelstam formula both are well established on relativistic
quantum field theory. Furthermore the components in
Bc meson and charmonium etc are heavy quarks i.e. the
nature of the components is non-relativistic, so the BS
equation is deduced into an instantaneous one in the ap-
1
With the equation, the spectrum and relevant wave function as
an eigenvalue problem derived from the BS equation can be computed.
arXiv:1411.3414v1 [hep-ph] 13 Nov 2014
Determining Compositeness of Hadronic Resonances: the
Λ(1405) Radiative Decay and the a0(980)- f0(980) Mixing
T. Sekihara1 and S. Kumano2,3
1
Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka, 567-0047, Japan
KEK Theory Center, Institute of Particle and Nuclear Studies, High Energy Accelerator Research
Organization (KEK), 1-1, Oho, Tsukuba, Ibaraki 305-0801, Japan
3
J-PARC Branch, KEK Theory Center, Institute of Particle and Nuclear Studies, High Energy
Accelerator Research Organization (KEK), 203-1, Shirakata, Tokai, Ibaraki, 319-1106, Japan
2
E-mail: [email protected]
(Received October 3, 2014)
Recently the concept of compositeness has been developed so as to distinguish whether interested
¯ molecuhadrons are hadronic molecules or not. Here, in terms of compositeness, we investigate KN
lar structure of the Λ(1405) resonance with the Λ(1405) radiative decay and K K¯ molecular structure
of the a0 (980) and f0 (980) resonances with the a0 (980)- f0(980) mixing.
KEYWORDS: hadronic molecules, compositeness, Λ(1405) radiative decay, a0 (980)- f0 (980)
mixing
1. Introduction
Although excellent successes of the constituent quark model tell us that ordinary hadrons consist
of three quarks (qqq) for baryons and a quark-antiquark pair (qq)
¯ for mesons [1], there should exist
exotic hadrons, which are not able to be classified as qqq for baryons and qq¯ for mesons since the
fundamental theory of strong interaction, QCD, does not prohibit such exotic systems as long as
they are color singlet. In fact, there are several experimental indications that some hadrons do not fit
into the classifications by the constituent quark model. For instance, the hyperon resonance Λ(1405)
has an anomalously light mass among the negative parity baryons and has been expected to be a
¯ molecular state rather than a three-quark state [2]. Moreover, the lightest scalar meson nonet
KN
shows inverted spectrum from the expectation with the qq¯ composition and hence various exotic
configurations have been proposed for the scalar mesons such as compact tetra-quark states [3] or
K K¯ molecules for a0 (980) and f0 (980) [4]. In addition, it is encouraging that charged quarkoniumlike states were observed in the heavy-quark sector by the Belle collaboration [5].
Among exotic hadrons, hadronic molecules are of special interest since they are unique in that
their constituents are not quarks but hadrons themselves, which will give various characteristic properties to hadronic molecules. For instance, a hadronic molecule can be a spatially extended object
due to the absence of strong quark confining force. Actually, spatial size of Λ(1405) was theoretically studied in Refs. [6–8] and it was found that its spatial size largely exceeds the typical hadronic
size . 0.8 fm. Furthermore, the uniqueness of hadronic molecules allows us to construct their twobody wave functions in terms of the hadronic degrees of freedom, and recently compositeness was
introduced as the contribution from the two-body wave function to the normalization of the total
wave function for hadrons so as to identify hadronic molecules [9–12]. Since the compositeness can
be evaluated from experimental observables, there is a possibility to determine experimentally the
structure of candidates of hadronic molecules such as Λ(1405).
State of new physics in b → s transitions
Wolfgang Altmannshofera and David M. Straubb
a
Perimeter Institute for Theoretical Physics, 31 Caroline St. N, Waterloo, Ontario, Canada N2L 2Y5
b
Excellence Cluster Universe, TUM, Boltzmannstr. 2, 85748 Garching, Germany
arXiv:1411.3161v1 [hep-ph] 12 Nov 2014
E-mail: [email protected], [email protected]
We present results of global fits of all relevant experimental data on rare b → s
decays. We observe significant tensions between the Standard Model predictions
and the data. After critically reviewing the possible sources of theoretical uncertainties, we find that within the Standard Model, the tensions could be explained if
there are unaccounted hadronic effects much larger than our estimates. Assuming
hadronic uncertainties are estimated in a sufficiently conservative way, we discuss
the implications of the experimental results on new physics, both model independently as well as in the context of the minimal supersymmetric standard model
and models with flavour-changing Z 0 bosons. We discuss in detail the violation
of lepton flavour universality as hinted by the current data and make predictions
for additional lepton flavour universality tests that can be performed in the future.
We find that the ratio of the forward-backward asymmetries in B → K ∗ µ+ µ− and
B → K ∗ e+ e− at low dilepton invariant mass is a particularly sensitive probe of
lepton flavour universality and allows to distinguish between different new physics
scenarios that give the best description of the current data.
Contents
1. Introduction
2
2. Observables and uncertainties
2.1. Effective Hamiltonian . . . .
2.2. B → Kµ+ µ− . . . . . . . . .
2.3. B → K ∗ µ+ µ− and B → K ∗ γ
2.4. Bs → φµ+ µ− . . . . . . . . .
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3
3
4
6
8
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9
9
10
15
17
18
4. Constraints on new physics models
4.1. General MSSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2. Flavour changing Z 0 bosons . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
21
26
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3. Global numerical analysis
3.1. Fit methodology . . . . . . . . . . . . . .
3.2. Compatibility of the data with the SM . .
3.3. New physics in a single Wilson coefficient
3.4. Constraints on pairs of Wilson coefficients
3.5. Testing lepton flavour universality . . . .
1
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Nuclear Physics B
Proceedings
Supplement
Nuclear Physics B Proceedings Supplement 00 (2014) 1–6
Measurements of the hadronic activity and the electroweak production in events
with a Z boson and two jets in proton-proton collisions with the CMS experiment
Paolo Azzurri, for the CMS Collaboration
arXiv:1411.3700v1 [hep-ex] 13 Nov 2014
INFN Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
Abstract
√
The observation of the electroweak production of a Z boson with two jets in pp collisions at s = 8 TeV with the
CMS experiment at the CERN LHC is presented, based on a data sample with an integrated luminosity of 19.7 fb−1 .
The cross section measurement, combining the muon and electron channels, is in agreement with the theoretical
expectations. Radiation patterns of selected Z plus two jets events, and the hadronic activity in the rapidity interval
between the jets are also measured. These results are of substantial importance in the more general study of vector
boson fusion processes, of relevance for Higgs boson searches and for measurements of electroweak gauge couplings
and vector boson scattering.
1. Introduction
In proton collisions at the LHC Vector Boson Fusion
(VBF) happens when a valence quark of each one of the
colliding protons radiates a W or Z boson that subsequently interact or “fuse”. For both valence quark radiating the weak bosons a t-channel four-momentum with
Q2 ∼ m2Z , m2W is exchanged. In this way the two valence quarks are typically scattered away from the beam
line and inside the detector acceptance, where they can
be revealed as hadronic jets. The distinctive signature
of VBF is therefore the presence of these two energetic
hadronic jets (tagging jets), roughly in the forward and
backward direction with respect to the proton beam line.
The VBF production has a great prominence at the
LHC for its importance for the measurements of the
Higgs sector couplings [1, 2]. The study of the VBF
production of Z or W bosons is therefore an important
benchmark to cross-check and validate Higgs VBF measurements [3], but serves further as a probe of triplegauge-boson couplings [4], for searches for physics beyond the standard model [5, 6], and as a precursor to the
measurement of elastic vector boson pair scattering.
On the other hand the VBF production of Z or W
bosons has some intriguing differences with respect to
the Higgs VBF productions. When focusing on VBF
Z/W production, the observed final state is composed of
a pair of fermions (ff), either quarks or leptons, from the
Z/W decay, associated with a pair of quarks (qq) from
the VBF production mechanism; but in this context
there is a large number of non-VBF diagrams that lead
to identical ffqq final states that can’t be neglected [7].
Considering only the classes of diagrams with purely
electroweak (EW) interactions, (like the VBF one),
shown in Figure 1, and no QCD interactions, the additional diagrams have strong negative interferences with
the VBF productions. These large negative interference
effects are in fact related to well-known non-abelian
gauge cancellations that preserve the scattering unitarity
and the electroweak model theory renormalizability [8].
This situation makes the VBF Z/W channel more complicated but also more interesting.
Another main scope of selecting “VBF-like” Z plus
two jets events, is to study the event hadronization properties connected with the peculiar VBF production color
structure. In VBF processes and more in general also
for the contributing electroweak processes with identical final states, there is no t-channel color exchange.
This leads to the expectation of a “rapidity gap” of
Measurement of CP Violation in B0s → J/ψ φ decays with the CMS detector.
Presented at the 8th International Workshop on the CKM Unitarity Triangle (CKM 2014),
Vienna, Austria, September 8-12, 2014
Jacopo Pazzini1 on behalf of the CMS collaboration.
arXiv:1411.3560v1 [hep-ex] 13 Nov 2014
1 Università
di Padova, INFN sezione di Padova
Abstract. The CP-violating weak phase φs and the decay width difference ∆Γs of B0s mesons are measured by the CMS experiment at the LHC using a data sample of B0s → J/ψ (µµ) φ (KK) decays. The
analysed dataset corresponds to an integrated luminosity of about 20 fb−1 collected in pp collisions
√
at a centre-of-mass energy s = 8 TeV. A total of 49 000 reconstructed B0s decays are used to extract
the values φs and ∆Γs by performing a time-dependent and flavour-tagged angular analysis of the
µ+ µ− K+ K− final state. The weak phase is measured to be φs = −0.03 ± 0.11 (stat.) ± 0.03 (syst.) rad,
and the decay width difference between the B0s mass eigenstates is ∆Γs = 0.096 ± 0.014 (stat.) ±
0.007 (syst.) ps−1 .
1 Introduction
Neutral B mesons are subject to mixing, i.e., oscillations from particle to antiparticle through flavour
changing neutral currents quark transition that
change the meson flavour by two units, ∆B = 2.
The B0s mixing is characterized by the mass difference ∆ms and by the decay width difference ∆Γs between the heavy (B H ) and light (B L ) mass eigenstates. A CP-violating phase φs arise from the interference between direct B0s meson decays into a
b → c¯cs CP eigenstate, and decays mediated by mixing to the same final state. The two corresponding phases φsD and φsM depend on the convention
of the CKM matrix parameterization. However,
the difference φs is phase-independent, and neglecting penguin diagram contributions, it is related to
the elements of the CKM matrix, as: φs ' −2β s ,
∗ ). A value of φ '
where β s = arg(−Vts Vtb∗ /Vcs Vcb
s
+0.0016
2β s = 0.0363−0.0015 rad, is predicted by the standard model (SM), determined via a global fit to experimental data [1]. Since the value is small and
precisely predicted, any deviation of the measured
value would be particularly interesting as a possible
hint of physics beyond the SM, contributing in the
B0s mixing. The decay width difference ∆Γs is predicted to be non-zero in the SM, and the theoretical
prediction, assuming no new physics in B0s mixing,
is ∆Γs = 0.087 ± 0.021 ps−1 [2]. In this measurement the B0s → J/ψ (µµ) φ (KK) decay channel has
a non-definite CP final state, and an angular analysis is therefore applied to disentangle the CP-odd
and CP-even components. A time-dependent angular analysis is performed with the CMS detector [3]
by measuring the decay angles of the final state particles µ+ µ− K+ K− , and the proper decay length of
the B0s . In this measurement the transversity basis
is used [4]. The angles θ T and ϕ T are the polar and
azimuthal angles of the µ+ in the rest frame of the
J/ψ, respectively, where the x axis is defined by the
direction of the φ (1020) meson in the J/ψ rest frame,
and the x-y plane is defined by the decay plane of
the φ (1020) → K+ K− . The helicity angle ψT is the
angle of the K+ in the φ (1020) rest frame with respect to the negative J/ψ momentum direction. The
differential decay rate of the B0s → J/ψ φ in terms of
proper decay length and angular variables is represented according to Ref. [5], as:
10
d4 Γ(B0s )
= f (Θ, α, ct) ∝ ∑ Oi (α, ct) · gi (Θ),
dΘdct
i =1
(1)
where Oi are the time-dependent functions, gi are
the angular functions, Θ represents the angles, and
ct represents the proper decay length of the B0s meson. A detailed description of the signal model can
be found in Ref. [6].
2 Event selection and simulated samples
The analized events are selected with a trigger optimized for the detection of b-hadrons decaying to
J/ψ(µ+ µ− ), with a dimuon invariant mass within
the range [2.9 − 3.3] GeV, and transverse momentum (pT ) greater than 6.9 GeV. The muon trajectories are fit to a common decay vertex, and the transverse decay length significance L xy /σLxy is required
arXiv:1411.3544v1 [hep-ex] 13 Nov 2014
SNSN-323-63
November 14, 2014
Top quark charge asymmetry measurements with
ATLAS detector
Umberto De Sanctis, on behalf of the ATLAS Collaboration
Department of Physics and Astronomy
University of Sussex, Brighton, Sussex, BN1 9QH, United Kingdom
PRESENTED AT
International Workshop on the CKM Unitarity Triangle
(CKM2014)
Wien, Austria, September 8–12, 2014
1
Introduction
Since its discovery in 1995, the top quark is playing a key role in the understanding
of Quantum Chromodynamics (QCD) processes at high energies. The top quark
pair(tt) production cross-section at the LHC allows to deeply explore the production
mechanisms and search for signals of New Physics processes beyond the Standard
Model (SM). In this article, the top quark charge asymmetry measurements performed
by the ATLAS [1] experiment are presented. Results in single-lepton and dilepton top
decay channels for pp collisions at 7 TeV center-of-mass energy using data collected
in 2011 are shown.
2
The top quark charge asymmetry
At the LHC collider, tt pairs are produced mainly through gluon-gluon (gg) fusion
process. Only around 20% of the events are produced from quark-antiquark (qq)
hard collisions, while the fraction coming from quark-gluon (qg) partonic processes
is almost negligible. The charge asymmetry AC is a manifestation of the forwardbackward asymmetry when the CP invariance holds. It is a tiny NLO QCD effect
(ASM
= 0.0123±0.0005 [2]) present only in asymmetric initial states, like qq and qg.
C
In the tt-system center-of-mass frame, the effect of the charge asymmetry is that tops
(antitops) are produced preferentially in the incoming quark (antiquark) direction. At
hadron colliders it is difficult to determine the quark/antiquark direction, so another
quantity in the laboratory frame is needed to measure this asymmetry. The variable
∆y = yt − yt , where y represents the rapidity of the top/antitop quark, measured
in the laboratory frame, is Lorentz invariant. It has the same value as the forwardbackward asymmetry in the tt center-of-mass frame, computed as a function of the
cos θ∗ angle between the top and the incoming quark. TeVatron experiments used
∆y variable to measure this asymmetry, counting the number of events where ∆y is
positive or negative.
At the LHC, due to the symmetry of the incoming beams, an asymmetry based on
the ∆y variable would vanish. Hence the variable ∆|y| = |yt | − |yt | has been chosen,
based on the fact that quarks are more boosted than antiquarks, due to the different
mean momenta carried by valence quarks and sea antiquarks. The asymmetry AC
obtained counting the number of events where ∆|y| is positive or negative, is called
top quark charge asymmetry.
3
Measurements in the single-lepton channel
The top quark charge asymmetry AC has been measured by the ATLAS experiment
with data collected at 7 TeV center-of-mass energy corresponding to an integrated
1
ATL-PHYS-PROC-2014-247
November 14, 2014
arXiv:1411.3521v1 [hep-ex] 13 Nov 2014
Searches with Boosted Objects
Katharina Behr
On behalf of the ATLAS and CMS Collaborations
Sub-department of Particle Physics, University of Oxford,
Keble Road, Oxford, OX1 3RH, United Kingdom
Boosted objects - particles whose transverse momentum is greater than
twice their mass - are becoming increasingly important as the LHC continues to explore energies in the TeV range. The sensitivity of searches
for new phenomena beyond the Standard Model depends critically on the
efficient reconstruction and identification (“tagging”) of their unique detector signatures. This contribution provides a review of searches for new
physics carried out by the ATLAS and CMS experiments that rely on the
reconstruction and identification of boosted top quarks as well as boosted
W , Z and Higgs bosons. A particular emphasis is placed on the different
substructure techniques and tagging algorithms for top quarks and bosons
employed by the two experiments.
PRESENTED AT
XXXIV Physics in Collision Symposium
Bloomington, Indiana, September 16–20, 2014
1
Introduction
Despite its tremendous success - once again impressively demonstrated by the discovery of the long-predicted Higgs Boson in 2012 - the Standard Model (SM) of particle
physics is widely considered an incomplete theory. For one, it cannot explain the fact
that the mass of the Higgs boson is light (hierarchy problem) nor does it offer a candidate for dark matter or satisfactorily explain the matter-antimatter asymmetry in
the observed universe. Hence a number of extensions to the SM have been proposed
whose predictions are currently under scrutiny by the LHC experiments. These extensions include theories with warped extra-dimensions (Randall-Sundrum models),
new strong interactions (Technicolour and others), an additional quark generation or
vector-like quarks as well as supersymmetry. (For details of the specific models see
the references in Sections 3, 4, 5 and references therein.) Many of these models
predict the existence of new heavy particles with large branching fractions into top
quarks, heavy gauge bosons or the Higgs boson. If these new states are sufficiently
heavy their decay products are likely to have transverse momenta exceeding twice
their rest masses. These decay products are called boosted objects.
The sensitivity of searches for new phenomena at high energies depends critically
on the efficient reconstruction and identification of boosted object decays. Boosted
techniques first were applied in searches at the Tevatron (see [1] for a recent review)
and developed into a fast growing field of research during Run I (2010-2012) of the
LHC, as its higher center-of-mass energies of 7 TeV (2011) and 8 TeV (2012) allow for
abundant production of boosted objects across many final states. This enabled the
experiments to push the exclusion limits for many new particles into the TeV regime.
This document provides a review of the most recent searches with boosted objects
carried out by the ATLAS [2] and CMS [3] experiments and presents some of the
most commonly used reconstruction and identification techniques. The rapid growth
of the field makes it impossible to cover every single technique within the scope of this
document. More details can be found in the proceedings of the BOOST workshop [1].
2
Large-R Jets and Substructure
The defining property of boosted object decays is the fact that their decay products
appear collimated in the momentum direction of the boosted mother particle in the
rest frame of the detector. Their angular separation ∆R is inversely proportional
to the transverse momentum pT of the mother particle with mass m according to a
simple rule of thumb:∗ ∆R ≈ 2m/pT . Figure 1(a) illustrates this for the boosted
p
∗
∆R = ∆η 2 + ∆φ2 with pseudorapidity η = -ln tan(θ/2). θ (φ) is the polar (azimuthal) angle
of the ATLAS/CMS standard coordinate system, a right-handed orthogonal system with the z-axis
tangential to the beam pipe and the nominal interaction point in the detector centre as its origin.
1
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP/2014-265
2014/11/14
arXiv:1411.3441v1 [hep-ex] 13 Nov 2014
CMS-HIG-14-018
Constraints on the spin-parity and anomalous HVV
couplings of the Higgs boson in proton collisions at 7 and
8 TeV
The CMS Collaboration∗
Abstract
The study of the spin-parity and tensor structure of the interactions of the recently
discovered Higgs boson is performed using the H → ZZ, Zγ∗ , γ∗ γ∗ → 4`, H →
WW → `ν`ν, and H → γγ decay modes. The full dataset recorded by the CMS
experiment during the LHC Run 1 is used, corresponding to an integrated luminosity of up to 5.1 fb−1 at a center-of-mass energy of 7 TeV and up to 19.7 fb−1 at 8 TeV.
A wide range of spin-two models is excluded at a 99% confidence level or higher,
or at a 99.87% confidence level for the minimal gravity-like couplings, regardless of
whether assumptions are made on the production mechanism. Any mixed-parity
spin-one state is excluded in the ZZ and WW modes at a greater than 99.999% confidence level. Under the hypothesis that the resonance is a spin-zero boson, the tensor
structure of the interactions of the Higgs boson with two vector bosons ZZ, Zγ, γγ,
and WW is investigated and limits on eleven anomalous contributions are set. Tighter
constraints on anomalous HVV interactions are obtained by combining the HZZ and
HWW measurements. All observations are consistent with the expectations for the
standard model Higgs boson with the quantum numbers J PC = 0++ .
Submitted to Physical Review D
c 2014 CERN for the benefit of the CMS Collaboration. CC-BY-3.0 license
∗ See
Appendix A for the list of collaboration members
Matrix elements of ∆B = 0 operators in heavy hadron chiral
perturbation theory
Jong-Wan Lee∗
Department of Physics, The City College of New York, New York, NY 10031, USA
(Dated: November 14, 2014)
arXiv:1411.3681v1 [hep-lat] 13 Nov 2014
Abstract
We study the light-quark mass and spatial volume dependence of the matrix elements of ∆B = 0
four-quark operators relevant for the determination of Vub and the lifetime ratios of single-b hadrons.
To this end, one-loop diagrams are computed in the framework of heavy hadron chiral perturbation theory with partially quenched formalism for three light-quark flavors in the isospin limit;
flavor-connected and -disconnected diagrams are carefully analyzed. These calculations include
the leading light-quark flavor and heavy-quark spin symmetry breaking effects in the heavy hadron
spectrum. Our results can be used in the chiral extrapolation of lattice calculations of the matrix
elements to the physical light-quark masses and to infinite volume. To provide insight on such chiral
extrapolation, we evaluate the one-loop contributions to the matrix elements containing external
Bd , Bs mesons and Λb baryon in the QCD limit, where sea and valence quark masses become equal.
In particular, we find that the matrix elements of the λ3 flavor-octet operators with external Bd
meson receive the contributions solely from connected diagrams in which current lattice techniques
are capable of precise determination of the matrix elements. Finite volume effects are at most a
few percent for typical lattice sizes and pion masses.
PACS numbers: 12.38Gc,12.39Fe,12.39Hg,14.20.Mr,14.40.Nd
Keywords:
∗
Electronic address: [email protected]
1
Quintessence with Yukawa Interaction
Andr´e A. Costaa ,∗ Lucas C. Olivaria ,† and E. Abdallaa‡
a
Instituto de F´ısica, Universidade de S˜
ao Paulo, C.P. 66318, 05315-970, S˜
ao Paulo, SP, Brazil
(Dated: November 14, 2014)
arXiv:1411.3660v1 [astro-ph.CO] 13 Nov 2014
We consider a quintessence model for dark energy interacting with dark matter via a Yukawa
interaction. To put constraints on this model we use the CMB measurements from the Planck
satellite together with BAO, SNIa and H0 data. We conclude that this is a viable model and an
appropriate scalar potential can favor the interacting scenario.
PACS numbers: 98.80.Es, 98.80.Jk, 95.30.Sf
I.
INTRODUCTION
Several cosmological observations, such as the measurement of the temperature anisotropies in the cosmic
microwave background (CMB) [1–4], the measurement
of the apparent magnitude of Type Ia supernovae (SNIa)
as a function of redshift [5], and the measurement of the
baryon acoustic oscillations (BAO) [6, 7], have demonstrated that the Universe is currently in an accelerated
phase of expansion and that its total energy budget is
dominated by a dark energy component. The nature of
dark energy is, despite years of intense investigations, an
unsolved problem, both under the theoretical and the
observational point of view.
The most straightforward candidate for dark energy is
the cosmological constant Λ, which has a constant equation of state parameter ω = −1. In the standard Λ-cold
dark matter (ΛCDM) model of the Universe, the cold
dark matter only interacts with other components gravitationally, while the dark energy is simply the vacuum
energy and therefore has no dynamics. This model fits
very well the current observational data, including the
recent Planck data [2–4]. Despite its experimental success, this model exhibits some theoretical shortcomings
such as the discrepancy between the value of the vacuum
energy obtained through observations and the theoretically estimated value [8]. This model also suffers from a
coincidence problem, i.e., why is the Universe dominated
by dark energy in late times [9, 10]?
Many alternative models for dark energy that attempt
to avoid the problems in the ΛCDM model have been
proposed in the literature. Most of them make use of
a dynamical field to describe the dark energy, such as
quintessence [11–13] and K-essence [14, 15]. Despite the
fact that none of these models actually solve the problems that plague the cosmological constant nor provide
a better fit to data than ΛCDM, some strong arguments
have been given to justify the use of dynamical dark energy models to describe the Universe [11–13].
The quintessence model is composed by a canonical
scalar field φ that slowly rolls down a potential energy
∗
†
‡
[email protected]
[email protected]
[email protected]
V (φ). In this case, the dark energy has a dynamical
equation of state ω and it can form large scale structures.
Also, for being a dynamic component, the quintessence
can naturally interact with other components of the Universe, such as the cold dark matter and neutrinos.
The idea that there is an interaction between dark energy and dark matter has a number of interesting properties from a cosmological point of view. First, it has
the theoretically appealing idea that the full dark sector
can be treated in a single framework. It can thus help
us alleviating the coincidence problem, since the dark
energy density now depends on the dark matter energy
density. Also an appropriate interaction can accommodate an effective dark energy equation of state in the
phantom region in the present time [16]. At last, the
interaction between dark energy and dark matter will affect significantly the expansion history of the Universe
and the evolution of density perturbations, which allows
us to constrain the parameters of such a model through
cosmological observations.
Cosmologies in which an interaction between dark energy and dark matter is present have been widely explored before in the literature, both at a phenomenological as well as at a Lagrangian level [17–32]. However,
most of the approaches that attempt to discuss an interacting dark sector at a Lagrangian level are built within
the framework of modified gravity [17, 33] or treat the
dark energy as an exotic form of matter [30, 31]. The
model that will be discussed in this work is, on the other
hand, built within the framework of a standard quantum
field theory in an attempt to be as simple as possible. To
accomplish this, we will treat the dark energy as a canonical scalar field, as the scalar field of the quintessence
model, and the dark matter as a spin 12 fermionic field.
We postulate that the dark energy interacts only with
the dark matter. Consequently, in our model, the baryonic matter evolves as in the ΛCDM model. This allows
us to avoid the fifth force problem that exists in some
interacting models [34]. We also postulate that the interaction in the dark sector is given by a Yukawa term
which couples the scalar and the fermionic fields. The
Yukawa interaction is renormalizable and well studied in
the literature, inclusive in cosmology [35, 36].
In order to constrain the cosmological parameters, we
make use of the latest high precision Planck data on CMB
temperature anisotropies together with the latest data
arXiv:1411.3658v1 [astro-ph.CO] 13 Nov 2014
Prepared for submission to JCAP
Can a spectator scalar field enhance
inflationary tensor mode?
Tomohiro Fujitaa,b Jun’ichi Yokoyamaa,c Shuichiro Yokoyamad
a Kavli
Institute for the Physics and Mathematics of the Universe (Kavli IPMU), WPI,
TODIAS, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8583, Japan
b Department of Physics, Graduate School of Science, The University of Tokyo, Bunkyo-ku
113-0033, Japan
c Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
d Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima, Tokyo, 2238521, Japan
E-mail: [email protected], [email protected],
[email protected]
Abstract. We consider the possibility of enhancing the inflationary tensor mode by introducing a spectator scalar field with a small sound speed which induces gravitational waves
as a second order effect. We analytically obtain the power spectra of gravitational waves and
curvature perturbation induced by the spectator scalar field. We found that the small sound
speed amplifies the curvature perturbation much more than the tensor mode and the current
observational constraint forces the induced gravitational waves to be negligible compared
with those from the vacuum fluctuation during inflation.
Keywords: inflation, primordial gravitational waves (theory)
Draft version November 14, 2014
Preprint typeset using LATEX style emulateapj v. 5/2/11
NEUTRINO AND COSMIC-RAY EMISSION AND CUMULATIVE BACKGROUND FROM
RADIATIVELY INEFFICIENT ACCRETION FLOWS IN LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI
Shigeo S. Kimura1 , Kohta Murase2 , and Kenji Toma3,4
arXiv:1411.3588v1 [astro-ph.HE] 13 Nov 2014
1 Department
of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
2 Hubble Fellow—Institute for Advanced Study, Princeton, New Jersey 08540, USA
3 Astronomical Institute, Tohoku University, Sendai 980-8578, Japan and
4 Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
Draft version November 14, 2014
ABSTRACT
We study high-energy neutrino and cosmic-ray emission from the cores of low-luminosity active
galactic nuclei (LLAGN). In LLAGN, the thermalization of particles is expected to be incomplete
in radiatively inefficient accretion flows (RIAFs), allowing the existence of non-thermal particles. In
this work, assuming stochastic particle acceleration due to turbulence in RIAFs, we solve the FokkerPlanck equation and calculate spectra of escaping neutrinos and CRs. The protons in RIAFs can
be accelerated up to & 10 PeV energies, and TeV-PeV neutrinos are generated via pp and/or pγ
reactions. We find that, if ∼ 1% of the accretion luminosity is carried away by non-thermal ions, the
diffuse neutrino intensity from the cores of LLAGN is as high as Eν2 Φν ∼ 3 × 10−8 GeV cm−2 s−1 ,
which can be compatible with the observed IceCube data. This result does not contradict either of
the diffuse gamma-ray background observed by Fermi or observed diffuse cosmic-ray flux. Our model
suggests that, although very-high-energy gamma rays may not escape, radio-quiet AGN with RIAFs
can emit GeV gamma-rays, which could be used for testing the model. We also calculate the neutron
luminosity from RIAFs of LLAGN, and discuss a strong constraint on the model of jet mass loading
mediated by neutrons from the diffuse neutrino observation.
Subject headings: acceleration of particles — accretion, accretion disks — galaxies: nuclei — neutrinos
— diffuse radiation
1. INTRODUCTION
The IceCube collaboration reported a discovery of extraterrestrial neutrinos with deposited energies ranging
from 30 TeV to a few PeV, and the significance now
exceeds 5σ (Aartsen et al. 2013a,b, 2014a). The signals are likely to be astrophysical, and the consistency
with isotropic distribution suggests extragalactic components, which is also supported by diffuse gamma-ray
data (Murase et al. 2013; Ahlers & Murase 2014). Significant clustering has not been observed, and the origin
of IceCube neutrinos is a new big mystery even though
some early models can match the observed data within
large model uncertainties (Anchordoqui et al. 2004;
Stecker 2005; Loeb & Waxman 2006; Murase et al. 2006;
Gupta & Zhang 2007; Murase et al. 2008; Kotera et al.
2009). One of the popular possibilities is neutrino emission from cosmic-ray (CR) reservoirs. Starburst galaxies
may explain the IceCube data, and various possibilities
have been speculated to have & 10−100 PeV CR protons
(Murase et al. 2013; Katz et al. 2013). Galaxy groups
and clusters may also account for the data without violating gamma-ray limits. While & 10−100 PeV CR protons
can be supplied by active galactic nuclei (AGN), galaxies
and galaxy mergers1 as well as intergalactic shocks, hard
spectral indices sν ∼ 2 and contributions from low-mass
clusters and groups would be needed 2 (Murase et al.
[email protected]
1 CR sources like AGN and galaxies strongly evolve as redshifts.
2 While neutrino and gamma-ray flux calculations by the recent work by Zandanel et al. (2014) is actually consistent with
Murase et al. (2008, 2009) for the massive cluster shock case, the
setup noted in Murase et al. (2013) has not been tested. Con-
2013; Kashiyama & M´esz´
aros 2014). However, due to
multi-messenger constraints (Murase et al. 2013), the
above scenarios may be challenged by the latest data
implying steep indices sν ∼ 2.3 − 2.5 (Aartsen et al.
2014a,b) and models that attribute the diffuse gammaray background to unresolved blazars.
High-energy neutrino production in AGN has been of
interest for many years (e.g., Protheroe & Kazanas
1983;
Kazanas & Ellison
1986;
Stecker et al.
1991; Szabo & Protheroe 1994; Mannheim 1995;
Atoyan & Dermer 2001; Alvarez-Muniz & M´esz´
aros
2004; Anchordoqui et al. 2004). The most popular
possibility is photohadronic (pγ) neutrino production
in relativistic jets that are established as gamma-ray
sites (e.g., Mannheim 1995; Atoyan & Dermer 2001;
M¨
ucke & Protheroe 2001). The diffuse neutrino intensity of radio-loud AGN is typically dominated by
luminous blazars, in which external radiation fields
due to accretion disk, broadline and dust emission are
relevant (Murase et al. 2014). However, it has been
shown that the simple inner jet model has difficulty in
explaining the IceCube data, and additional assumptions are required (Dermer et al. 2014; Tavecchio et al.
2014). Alternatively, high-energy neutrino emission
could mainly come from the cores of AGN, and both
of pp (Becker Tjus et al. 2014) and pγ (Stecker 2013;
Winter 2013; Kalashev et al. 2014) scenarios have been
considered. In the latter case, it has been assumed that
necting individual massive cluster emission to diffuse backgrounds
depends on models and underlying assumptions, and astrophysical
uncertainty is still too large to cover all the relevant parameter
space.
Hadron structure from lattice QCD - outlook and
future perspectives
arXiv:1411.3495v1 [hep-lat] 13 Nov 2014
Constantia Alexandrou
Department of Physics, University of Cyprus, PO Box 20537, 1678 Nicosia, Cyprus,
Computation-based Science and Technology Research Center, Cyprus Institute, 20 Kavafi Str.,
Nicosia 2121, Cyprus,
NIC, DESY, Platanenallee 6, D-15738 Zeuthen, Germany
DOI: will be assigned
We review results on hadron structure using lattice QCD simulations with pion masses close
or at the physical value. We pay particular attention to recent successes on the computation
of the mass of the low-lying baryons and on the challenges involved in evaluating energies
of excited states and resonance parameters as well as in studies of nucleon structure.
1
Introduction
An impressive progress in algorithms and increased computational resources have allowed lattice
QCD simulations with dynamical quarks with masses fixed at their physical values. Such
simulations remove the need for a chiral extrapolation, thereby eliminating a significant source
of a systematic uncertainty that has proved difficult to quantify in the past. However, new
challenges are presented: An increase of statistical noise leads to large uncertainties on most
of the observables of interest. New approaches to deal with this problem are being developed
that include better algorithms to speed up the computation of the quark propagators as well
as efficient (approximate) ways to increase the statistics. Another challenge is related to the
fact that most of the particles become unstable if the lattice size is large enough and methods
to study decays on a finite lattice in Euclidean time need further development.
In this talk we review recent results on hadron structure obtained using improved discretization schemes, notably Wilson-type fermion actions and domain wall fermions. In particular, the
Wilson-type twisted mass fermion (TMF) action is particularly suitable for hadron structure
studies, mainly due to the automatic O(a) improvement, where a is the lattice spacing. Several TMF ensembles have been produced including an ensemble simulated with two degenerate
light quarks (Nf = 2) with mass fixed to their physical value, which for technical reasons, also
includes a clover term in the action but avoids smearing of the gauge links [1]. We will refer to
this ensemble as the ’physical point ensemble’ for which we will present a number of new results.
The other TMF ensembles are simulated with light quarks having masses larger than physical
but where simulations are performed for three values of a allowing to study the dependence
on the lattice spacing and to take the continuum limit. These ensembles include simulations
with strange and charm quarks in the sea (Nf = 2 + 1 + 1) besides Nf = 2 TMF ensembles.
In particular, we will use an Nf = 2 + 1 + 1 ensemble having a pion mass mπ = 373 MeV
PANIC14
1
Nucleon observables and axial charges of other
baryons using twisted mass fermions
Constantia Alexandrou ∗
arXiv:1411.3494v1 [hep-lat] 13 Nov 2014
Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus,
Computation-based Science and Technology Research Center, Cyprus Institute, 20 Kavafi Str.,
Nicosia 2121, Cyprus,
NIC, DESY, Platanenallee 6, D-15738 Zeuthen, Germany
E-mail: [email protected]
Martha Constantinou
Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
E-mail: [email protected]
Kyriakos Hadjiyiannakou
Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
E-mail: [email protected]
Karl Jansen
NIC, DESY, Platanenallee 6, D-15738 Zeuthen, Germany
E-mail: [email protected]
Christos Kallidonis
Computation-based Science and Technology Research Center, Cyprus Institute, 20 Kavafi Str.,
Nicosia 2121, Cyprus
E-mail: [email protected]
Giannis Koutsou
Computation-based Science and Technology Research Center, Cyprus Institute, 20 Kavafi Str.,
Nicosia 2121, Cyprus
E-mail: [email protected]
We present results on the nucleon scalar, axial and tensor charges, as well as, on the first moments
of the unpolarized, polarized and transversity parton distributions using N f = 2 and N f = 2+1+1
twisted mass fermions. These including an ensemble that yields the physical value of the ratio of
the nucleon to the pion mass. Results on the axial charges of hyperons and charmed baryons are
also presented for a range of pion masses including the physical one.
32nd International Symposium on Lattice Field Theory - LATTICE 2014
23-28 June, 2014
Columbia University New York, NY
∗ Speaker.
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Constantia Alexandrou
Nucleon observables and axial charges of other baryons
1. Introduction
We evaluate fundamental properties of the nucleon within the fermion twisted mass formulation of lattice QCD. The scalar, axial and tensor charges are computed using a number of twisted
mass fermion (TMF) ensembles including one simulated with light quark mass fixed to their physical value. The computation of the nucleon axial charges allows a direct comparison with experiment, while determining the values of the scalar and tensor couplings provide useful input for
searches beyond the familiar weak interactions of the Standard Model sought in the decay of ultracold neutrons.The computation of the tensor charge is particularly timely since new experiments
using polarized 3 He/Proton at Jefferson lab aim at increasing the experimental accuracy by an order of magnitude [1]. Using N f = 2 and N f = 2 + 1 + 1 ensembles of TMF with lattice spacings
smaller than 0.1 fm [2] we compute nucleon matrix elements at zero momentum transfer. The
twisted mass formulation is well-suited for hadron structure calculations since it provides automatic O(a2 ) improvement requiring no operator modification [3]. Our results include a simulation
using the Iwasaki gluon action, and N f = 2 TMF with a clover term yielding the physical value of
the pion mass, on a lattice of size 483 × 96, referred to as the physical ensemble [4].
Using similar techniques as those for the case of the nucleon, we also compute the axial
charges of hyperons and charmed baryons on the same ensembles. The values of the axial charges
of these particles are either poorly measured or not known and thus lattice QCD provides valuable
input needed for phenomenological models.
2. Hadron spectrum
1.8
1.7
1.6
3.8
ETMC Nf=2 with CSW
BMW Nf=2+1
PACS-CS Nf=2+1
3.6
3.4
M (GeV)
1.5
5
ETMC Nf=2 with CSW
PACS-CS Nf=2+1+1
Na et al. Nf=2+1
Briceno et al. Nf=2+1+1
Liu et al. Nf=2+1
4.5
1.4
3
1.3
1.2
2.8
1.1
2.6
1
2.4
0.9
N
Λ
Σ
Ξ
Δ
Σ*
Ξ*
Ω
2.2
ETMC Nf=2 with CSW
PACS-CS Nf=2+1+1
Na et al. Nf=2+1
Briceno et al. Nf=2+1+1
4
3.2
3.5
3
2.5
Λc
Σc
Ξ'c
Ξc
Ωc
Ξcc
Ωcc
Σ*c
Ξ*c
Ω*c
Ξ*cc
Ω*cc
Ωccc
Figure 1: Results on baryon masses using the physical ensemble. Left: The octet and decuplet (the Ω and Ξ
were discovered at Brookhaven 50 years ago [7]). Spin-1/2 (middle) and spin-3/2 (right) charmed baryons.
Before discussing the structure of baryons we need to compute their mass. In Refs. [5, 6] the
masses of baryons were investigated using N f = 2 and N f = 2 + 1 + 1 TMF ensembles for three
lattice spacings and a range of pion masses the smallest one being 210 MeV. Here, we present
results computed for the physical ensemble. The lattice spacing is a = 0.094(1) fm determined
from the nucleon mass. The strange and charm quark mass are fixed by using the Ω and Λc mass,
respectively. The resulting masses for the strange and charmed baryons are shown in Figs. 1.
Although the continuum limit is not yet performed we observe agreement with the experimental
values, as well as, with the values of other collaborations. Our previous study suggests that discretization errors are small and this may explain agreement with experiment even at a finite value
of a. Assuming negligible cut-off effects, we can give a values for the yet non-measured mass of
the charmed baryons. We find for the mass of Ξ∗cc 3.678(8) GeV, for the Ω+
cc 3.708(10) GeV, for
++
Ω∗+
cc 3.767(11) GeV and for Ωccc 4.746(3) GeV.
2
LAPTH-226/14
Millisecond pulsars and the Galactic
Center gamma-ray excess: the
importance of luminosity function
and secondary emission
arXiv:1411.2980v1 [astro-ph.HE] 11 Nov 2014
Jovana Petrovi´
c a,b , Pasquale D. Serpico c , Gabrijela Zaharijas d,e,f
a
Department of Astronomy, Faculty of Mathematics, University of Belgrade, Studentski
trg 16 , 11000 Beograd, Serbia
b
c
Department of Physics, Faculty of Sciences, University of Novi Sad, Trg Dositeja
Obradovi´ca 4, 21000 Novi Sad, Serbia
Laboratoire de Physique Th´eorique d’ Annecy-le-Vieux (LAPTh), Univ. de Savoie,
CNRS, B.P.110, Annecy-le-Vieux F-74941, France
d
Laboratory for Astroparticle Physics (LAPP),
University of Nova Gorica, Vipavska 13, SI-5000 Nova Gorica, Slovenia
e
Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11,
34151 Trieste, Italy
f
Istituto Nazionale di Fisica Nucleare - Sezione Trieste (INFN),
Padriciano 99, I - 34149 Trieste, Italy
Abstract
Recently, several groups of authors have analyzed Fermi LAT data
in a region around the Galactic Center finding an unaccounted
gamma-ray excess over diffuse backgrounds in the GeV energy
range. Here we test the possibility that this excess is produced by
a population of yet unresolved millisecond pulsars (MSPs) located
in the bulge of the Milky Way. We rely on the MSP characteristics reported by the 2PC catalogue, use the package GALPLOT
to simulate this population, and compare our results to what has
been detected and flagged as “gamma ray excess”. We find that
the conclusions strongly depend on the details of the MSP luminosity function (in particular, its high luminosity end) as well
as on the possible secondary emission of the MSP population.
Within current uncertainties, a large if not dominant contribution
1
Prepared for submission to JHEP
CERN-PH-TH-2014-199, DFPD-2014/TH/16
arXiv:1411.2605v1 [hep-th] 10 Nov 2014
On sgoldstino-less supergravity models of inflation
Gianguido Dall’Agataa and Fabio Zwirnera,b
a
Dipartimento di Fisica e Astronomia ‘G. Galilei’, Università di Padova
and INFN, Sezione di Padova, Via Marzolo 8, I-35131 Padova, Italy
b
Theory Unit, Physics Department, CERN, CH-1211 Genève 23, Switzerland
E-mail: [email protected], [email protected]
Abstract: We go a step further in the search for a consistent and realistic supergravity
model of large-field inflation by building a class of models with the following features:
during slow-roll, all the scalar fields other than the inflaton are frozen by large inflatondependent masses or removed from the spectrum; at the end of inflation, supersymmetry is
spontaneously broken with naturally vanishing classical vacuum energy. We achieve this by
combining some geometrical properties of the Kähler potential with the consistent use of
a single nilpotent chiral superfield, in one-to-one correspondence with the supersymmetrybreaking direction in field space at the vacuum.
arXiv:1411.3683v1 [hep-ph] 28 Oct 2014
Prepared for submission to JCAP
Effective scalar four-fermion
interaction for Ge–phobic exothermic
dark matter and the CDMS-II Silicon
excess
Stefano Scopel,a Jong-Hyun Yoonb
Department of Physics, Sogang University, Seoul, South Korea
E-mail: [email protected], [email protected]
Abstract. We discuss within the framework of effective four–fermion scalar interaction the
phenomenology of a Weakly Interacting Massive Particle (WIMP) Dirac Dark Matter candidate which is exothermic (i.e. is metastable and interacts with nuclear targets down–
scattering to a lower–mass state) and Ge–phobic (i.e. whose couplings to quarks violate
isospin symmetry leading to a suppression of its cross section off Germanium targets). We
discuss the specific example of the CDMS–II Silicon three-candidate effect showing that a
region of the parameter space of the model exists where WIMP scatterings can explain the
excess in compliance with other experimental constraints, while at the same time the Dark
Matter particle can have a thermal relic density compatible with observation. In this scenario
the metastable state χ and the lowest–mass one χ′ have approximately the same density in
the present Universe and in our Galaxy, but direct detection experiments are only sensitive
to the down–scatters of χ to χ′ . We include a discussion of the recently calculated Next–to–
Leading Order corrections to Dark Matter–nucleus scattering, showing that their impact on
the phenomenology is typically small, but can become sizable in the same parameter space
where the thermal relic density is compatible to observation.
arXiv:1411.3682v1 [hep-ph] 13 Nov 2014
International Journal of Modern Physics: Conference Series
c The Authors
Sivers Asymmetry with QCD Evolution
MIGUEL G. ECHEVARRIA∗
Nikhef and Department of Physics and Astronomy, VU University Amsterdam,
Science Park 105, NL-1098 XG Amsterdam, the Netherlands
[email protected]
AHMAD IDILBI
Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
[email protected]
ZHONG-BO KANG
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
[email protected]
IVAN VITEV
Los Alamos National Laboratory, Los Alamos, NM 87545, USA
[email protected]
We analyze the Sivers asymmetry in both Drell-Yan (DY) production and semiinclusive deep inelastic scattering (SIDIS), while considering properly defined transverse
momentum dependent parton distribution and fragmentation functions and their QCD
evolution. After finding a universal non-perturbative spin-independent Sudakov factor
that can describe reasonably well the world’s data of SIDIS, DY lepton pair and W/Z
production in unpolarized scatterings, we perform a global fitting of all the experimental
data on the Sivers asymmetry in SIDIS from HERMES, COMPASS and Jefferson Lab.
Then we make predictions for the asymmetry in DY lepton pair and W boson production,
which could be compared to the future experimental data in order to test the sign change
of the Sivers function.
1. Introduction
Transverse spin physics has become a very active field of research both experimentally and theoretically, providing valuable information on the hadron substructure.
This information is encoded in the so-called transverse momentum dependent parton distribution and fragmentation functions (TMDPDF/TMDPFF)1,2 . One of the
most analyzed spin asymmetries is the Sivers effect, originated from a particular
∗ Speaker.
This is an Open Access article published by World Scientific Publishing Company. It is distributed
under the terms of the Creative Commons Attribution 3.0 (CC-BY) License. Further distribution
of this work is permitted, provided the original work is properly cited.
1
arXiv:1411.3680v1 [hep-ph] 28 Oct 2014
Review of QCD, Quark-Gluon Plasma, Heavy Quark
Hybrids, and Heavy Quark State production in p-p and
A-A collisions
Leonard S. Kisslinger1
Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213
Debasish Das2,3
Saha Institute of Nuclear Physics,1/AF, Bidhan Nagar, Kolkata 700064, INDIA.
1) [email protected]
2)[email protected]; 3) [email protected]
Abstract
This is a review of the Quantum Chrodynamics Cosmological Phase Transition,
the Quark-Gluon Plasma, and the detection of the Quark-Gluon Plasma via RHIC
production of heavy quark states using the mixed hybrid theory for the Ψ(2S) and
Υ(3S) states.
PACS Indices:12.38.Aw,13.60.Le,14.40.Lb,14.40Nd
Keywords: Quantum Chromodynamics,QCD Phase Transition, Quark-Gluon Plasma,
mixed hybrid theory
1
Outline of QCD Review
QCD Theory of the Strong Interaction
The QCD Phase Transition
Heavy Quark Mixed Hybrid States
Proton-Proton Collisions and Production of Heavy Quark States
RHIC and Production of Heavy Quark States
Production of Charmonium and Bottomonium States via Fragmentation
Brief Overview
2
Brief Review of Quantum Chromodynamics (QCD)
In the theory of strong interactions quarks, fermions, interact via coupling to gluons, vector
(quantum spin 1) bosons, the quanta of the strong interaction fields, color replaces the
electric charge in QED, which is why it is called Quantum Chromodynamics or QCD. See
Refs[1],[2],[3], and Cheng-Li’s book on gauge theories[4].
1
Anisotropic Jet Quenching in semi-Quark-Gluon Plasmas with Magnetic Monopoles
in Ultrarelativistic Heavy Ion Collisions
Jiechen Xu,1 Jinfeng Liao,2, 3 and Miklos Gyulassy1
1
arXiv:1411.3673v1 [hep-ph] 13 Nov 2014
2
Department of Physics, Columbia University, 538 West 120th Street, New York, NY 10027, USA
Physics Dept and CEEM, Indiana University, 2401 N Milo B. Sampson Lane, Bloomington, IN 47408, USA
3
RIKEN BNL Research Center, Bldg. 510A, Brookhaven National Laboratory, Upton, NY 11973, USA
(Dated: November 14, 2014)
We present a new jet quenching framework, CUJET3.0, that is shown to account well for both high
pT single inclusive hadron suppression RAA and its azimuthal anisotropy v2 in heavy ion collisions
at both RHIC and the LHC energies. CUJET3.0 generalizes our previous pQCD/HTL based CUJET2.0 model that couples running coupling DGLV jet energy loss to (2+1)D viscous hydrodynamic
backgrounds constrained by bulk flow observables. Version 3.0 reduces to 2.0 in the high temperatures T > 400 MeV limit, but it includes two new nonperturbative effects in the QCD transition
temperature range T ∼ 140−250 MeV: (1) the Polyakov loop suppression of color-electric scattering
(aka “semi-QGP” of Pisarski et al) and (2) the enhancement of scattering due to emergent magnetic
monopoles near Tc (aka “magnetic scenario” of Liao and Shuryak). The parameters of the model
are constrained by lattice QCD data and the jet medium coupling is matched to asymptotic freedom in the high temperature limit. We find that the CUJET3.0 jet transport parameter qˆ(E, T )/T 3
peaks near Tc by a factor ∼ 4 above previous perturbative CUJET2.0 estimates, approaching hybrid
AdS/SYM holography of Liu et al, but it has very strong nonconformal E and T dependence up to
T ∼ 400 MeV. Extrapolating down to E = 2 GeV, we find a striking new connection between bulk
perfect fluidity with η/s ∼ 0.1 near Tc and high pT high T perturbative jet quenching.
PACS numbers: 25.75.-q, 12.38.Mh, 24.85.+p, 13.87.-a
Introduction. The strong nuclear force in Nature is described in the Standard Model by Quantum Chromodynamics (QCD), a quantum field theory based on quarks
and gluons. These “building blocks” are deeply confined
in normal nuclear matter and only get liberated under
extremely hot and/or dense conditions. Such a deconfined quark-gluon plasma (QGP) was a primordial phase
of matter in the early Universe a few microseconds after the Big Bang. It has now been (re)created as a new
form of matter by ultrarelativistic heavy-ion collisions at
the BNL Relativistic Heavy Ion Collider (RHIC) and the
CERN Large Hadron Collider (LHC) [1–3].
In such collisions, highly energetic partons with large
transverse momentum (pT ) are occasionally produced at
the initial impact and subsequently penetrate the formed
hot QGP medium. Such partonic jets experience strong
scatterings with medium constituents, lose energy via radiative and collisional processes, and eventually fragment
into observed high pT hadrons with reduced yield as compared with proton-proton collisions at same energy but
without medium effect. This is the phenomenon of jet
quenching discovered at RHIC and LHC. The high pT
single inclusive jet fragment (e, π, D, B) observables of
the nuclear suppression factor RAA and its azimuthal
transverse anisotropy (characterized by its elliptic moment v2 ) have been measured at RHIC [4–7] and the LHC
[8–15], and have stimulating intensive theoretical studies
of jet quenching with varied approaches (for reviews, see
[16–21]). Some of the key issues we hope to learn from
jet quenching about the QGP medium include: What
are the effective degrees of freedom with which the jets
scatter? How strongly do they interact with jets? How
does the jet-medium interaction vary with jet energy and
medium temperature? And, most importantly, what can
we learn about the physics of QCD confinement?
Recent jet quenching studies have shown that the overall suppression RAA and its azimuthal anisotropy v2 at
both RHIC and LHC provide a stringent set of observables in constraining the jet-medium interactions. Qualitative insights of a reduced average opaqueness from
RHIC to LHC were first pointed out in [22–25] and more
recently a quantitative extraction of the jet transport
coefficient qˆ(E, T ) = hkT2 i/λ (the average jet-medium
momentum transfer square per unit path length) was
done by the JET collaboration [26]. The jet quenching anisotropy v2 arising from varied medium “thickness” along different azimuthal orientation [27] however
has remained a long standing puzzle that “fails” most
past models and there has lacked so far a more sophisticated jet quenching framework that can include both
perturbative as well as lattice QCD constraints and bulk
hydrodynamic constraints to account simultaneously both
RAA and v2 at both RHIC and LHC energies.
A novel nonperturbative resolution of the v2 puzzle
(already severe at RHIC, see e.g. [28]) was first proposed in [29], suggesting a strong enhancement of jetmedium interaction near the QCD transition temperature Tc in analogy to the “critical opalescence”. This
mechanism was further shown to significantly improve
the high pT v2 robustly in varied modeling implementations [23, 24, 30–32]. Recent CUJET2.0 study [33] found
a modest 10% variation of jet-medium coupling along
arXiv:1411.3666v1 [hep-ph] 13 Nov 2014
Exact solution of the (0+1)-dimensional
Boltzmann equation for massive
Bose-Einstein and Fermi-Dirac gases
Wojciech Florkowski
1
Institute of Physics, Jan Kochanowski University, PL-25406 Kielce, Poland
The H. Niewodnicza´
nski Institute of Nuclear Physics, Polish Academy of Sciences,
PL-31342 Krak´
ow, Poland
2
E-mail: [email protected]
Ewa Maksymiuk
Institute of Physics, Jan Kochanowski University, PL-25406 Kielce, Poland
E-mail: [email protected]
Abstract. We present the exact solution of the (0+1)-dimensional Boltzmann
equation for massive Bose-Einstein and Fermi-Dirac gases. For the initial conditions
used typically in ultra-relativistic heavy-ion collisions, we find that the effects
of quantum statistics are very small for thermodynamics-like functions such as
the effective temperature, energy density or transverse and longitudinal pressures.
Similarly, the inclusion of quantum statistics affects very little the shear viscosity.
On the other hand, the quantum statistics becomes important for description of the
phenomena connected with the bulk viscosity.
PACS numbers: 25.75.-q, 25.75.Dw, 25.75.Ld
Keywords: relativistic heavy-ion collisions, particle spectra, femtoscopy, LHC
Submitted to: J. Phys. G: Nucl. Phys.
arXiv:1411.3657v1 [hep-ph] 12 Nov 2014
Dark Atoms and their decaying constituents
3
K. Belotsky1,2 , M. Khlopov1,2,3 , M. Laletin1
1
National Research Nuclear University ”MEPHI”
(Moscow Engineering Physics Institute),
115409 Moscow, Russia
2
Centre for Cosmoparticle Physics “Cosmion”
115409 Moscow, Russia
APC laboratory 10, rue Alice Domon et L´eonie Duquet
75205 Paris Cedex 13, France
Abstract
The nonbaryonic dark matter of the Universe might consist of
new stable charged species, bound by ordinary Coulomb interactions
in various forms of heavy neutral ”dark atoms”. The existing models offer natural implementations for the dominant and subdominant
forms of dark atom components. In the framework of Walking Technicolor the charge asymmetric excess of both stable negatively doubly
charged technilepton ζ −− and metastable but longliving positively
doubly charged technibaryon U U ++ can be generated in the early
Universe together with the observed baryon asymmetry. If the excess
of ζ exceeds by several orders of magnitude the excess of U U , dark
matter might consist dominantly by Heζ dark atoms of nuclear interacting O-helium (OHe) bound state of ζ with primordial helium.
This dominant dark matter component causes negligible nuclear recoil in underground experiments, but can explain positive results of
DAMA/NaI and DAMA/LIBRA experiments by annual modulations
of few keV energy release in radiative capture of OHe by sodium.
However, a sufficiently small subdominant component of WIMP-like
objects U U ζ can also form. Making up a small fraction of dark matter,
it can also evade the severe constraints on WIMPs from underground
detectors. Although sparse, this subdominant component can lead to
observable effects, since leptonic decays of technibaryons U U give rise
to two positively charged leptons contrary to the pairs of opposite
charge leptons created in decays of neutral particles. We show that
decays of U U ++ → e+ e+ , µ+ µ+ , τ + τ + of the subdominant U U ζ component of dark matter, can explain the observed high energy positron
excess in the cosmic rays if the fraction of U U ζ is ∼ 10−6 of the total
dark matter density, the mass of U U ++ about 1 TeV and the lifetime
1
Stretched String with Self-Interaction at High Resolution:
Spatial Sizes and Saturation
Yachao Qian and Ismail Zahed1
arXiv:1411.3653v1 [hep-ph] 13 Nov 2014
1
Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800.
(Dated: November 14, 2014)
We model the (holographic) QCD Pomeron as a long and stretched (fixed impact parameter)
transverse quantum string in flat D⊥ = 3 dimensions. After discretizing the string in N string bits,
we analyze its length, mass and spatial distribution for large N or low-x (x = 1/N ), and away from
its Hagedorn point. The string bit distribution shows sizable asymmetries in the transverse plane
that may translate to azimuthal asymmetries in primordial particle production in the Pomeron
kinematics, and the flow moments in minimum bias pp and pA events. At moderately low-x and
relatively small string self-interactions gs ≈ αs (the gauge coupling), a pre-saturation phase is
identified whereby the string transverse area undergoes a first order transition from a large diffusive
growth to a small fixed size area set by few string lengths ls . This phase amounts to a saturation of
the cross section within the Froissart bound. For lower values of x the transverse string bit density
is shown to increase as 1/x before saturating at the Bekenstein bound of one bit per Planck area.
2/3
The Planck scale is identified as lP ≈ αs ls through holography.
I.
INTRODUCTION
Hadron-hadron collisions at high energies but soft momentum transfer are dominated by soft Pomeron exchange,
an effective 0++ exchange corresponding to the highest Regge trajectory with intercept αP (0) − 1 ≈ 0.08 [1]. Reggeon
exchanges with spin-isospin quantum numbers have smaller intercepts and are therefore sub-leading [2, 3]. The growth
of the total hadron-hadron cross-section with the rapidity interval χ = ln(s/s0 ) is described phenomenologically in
the context of Reggeon field theory. In QCD the re-summation of the soft collinear Bremmstralung contributions
through the BFKL ladders yield a hard Pomeron with a perturbatively small intercept and zero slope [4–8].
Soft Pomerons are altogether non-perturbative. Duality arguments put forth by Veneziano [9] suggest that the soft
Pomeron is a closed string exchange in the t-channel, with a string world-sheet made of planar diagrams like fishnets [10]. The quantum theory of planar diagrams in the double limit of strong coupling and large number of colors
is tractable in supersymmetric theories using the holographic principle [11]. Many descriptions of the soft Pomeron
in holographic duals to QCD have been suggested recently without supersymmetry [12–31]. A simple version is a
stringy exchange in AdS5 with a wall with D⊥ = 3 dimensions, that reproduces a number of features of diffractive
scattering, production and low-x DIS. Throughout and for simplicity, the curvature of AdS5 will be ignored.
The Pomeron as a string exchange in holography can be thought as a chain of closed but confined gluons, some
sort of non-perturbative Weizacker-Williams field tying two colorless dipoles separated by a large rapidity interval χ.
In this spirit, lepton on proton scattering in DIS at low-x can be described through a holographic string exchange
with the identification χ ≈ ln(1/x). In the proton rest frame, the leptonic dipole of size 1/Q acts as a small probe
dipole scattering off the larger dipole composing the proton at a fixed impact parameter b. DIS experiments are
always averaged over this impact parameter when measuring gluonic densities in structure functions. However, the
dominant contribution in the averaging stems from large b [27–29]. More exclusive experiments could be done in
future electron-Ion-Colliders to unravel the impact parameter dependence at low-x as well.
Low-x physics translates to a large N = 1/x resolution of the holographic string as we detail below. This is achieved
for long strings by discretizing the transverse Polyakov scalar action in N string bits and ignoring initially the stringy
interactions (free string). String bits have been identified with wee (gluonic) partons by Thorn [32, 33]. The slow
logarithmic growth of the free string transverse area translates to an anomalously large transverse string bit density
at low-x. Repulsive string interactions can cause the transverse density to conform with the maximum Bekenstein
bound for a black-hole as argued by Susskind for wee gravitons [16, 34, 35]. However, such a growth appears to be at
odd with the Froissart bound [36].
A high string bit density at low-x points towards a liquid of string bits, a priori resolving the string. However,
the underlying presence of the string is still paramount to maintain the (Gribov) diffusion of the string bits in the
transverse plane. Recall that the diffusion constant D = ls2 /2 is dimensionfull and ties with the squared string length.
Also, a highly resolved string provides an optimal desccription of low-x saturation in QCD as wee partons reaching
the Bekenstein bound [37–41]. In this work we will show that the bound is reached in two stages. First a dilute
pre-saturation stage where the string transverse area undergoes a first order transition from a large diffusive growth
to a small but fixed size set by the string scale for relatively weak string self-interactions. The cross section freezes
below the Froissart bound [36]. Second a dense saturation stage at very low-x whereby the transverse string bit
Interplay of Threshold Resummation and Hadron Mass Corrections
in Deep Inelastic Processes
Alberto Accardi a,b , Daniele P. Anderle c , Felix Ringer c
a
Hampton University, Hampton, VA 23668, USA
Jefferson Lab, Newport News, VA 23606, USA
c
T¨
ubingen University, 72076 T¨
ubingen, Germany
(Dated: November 14, 2014)
arXiv:1411.3649v1 [hep-ph] 13 Nov 2014
b
We discuss hadron mass corrections and threshold resummation for deep-inelastic scattering
ℓN → ℓ′ X and semi-inclusive annihilation e+ e− → hX processes, and provide a prescription how
to consistently combine these two corrections respecting all kinematic thresholds. We find an interesting interplay between threshold resummation and target mass corrections for deep-inelastic
scattering at large values of Bjorken xB . In semi-inclusive annihilation, on the contrary, the two
considered corrections are relevant in different kinematic regions and do not affect each other. A
detailed analysis is nonetheless of interest in the light of recent high precision data from BaBar
and Belle on pion and kaon production, with which we compare our calculations. For both deep
inelastic scattering and single inclusive annihilation, the size of the combined corrections compared
to the precision of world data is shown to be large. Therefore, we conclude that these theoretical
corrections are relevant for global QCD fits in order to extract precise parton distributions at large
Bjorken xB , and fragmentation functions over the whole kinematic range.
PACS numbers: 12.38.Bx, 13.85.Ni, 13.88.+e
I.
INTRODUCTION
Predictions from QCD rely on perturbative calculations of parton-level hard scattering processes as well
as on non-perturbative input in the form of parton distribution functions (PDFs) and fragmentation functions
(FFs). On the one hand, PDFs contain information
about the distributions of quarks and gluons in hadrons,
which is relevant for processes with initial-state hadrons.
On the other hand, FFs describe the fragmentation of
an outgoing parton into the observed hadron and, to
some extent, may be viewed as the final-state analogue
of PDFs. The applicability of this framework within
perturbative QCD was established in factorization theorems [1] allowing one to absorb long-distance dynamics
into these two universal non-perturbative objects. Therefore, the predictive power of QCD relies crucially on the
precise knowledge of PDFs and FFs, that are nowadays
extracted from a global analysis of a wide set of experimental data, see Refs. [2–4] for recent reviews.
Modern PDF fits [5–7] are available within a next-toleading order (NLO) framework and most of them also
at (partial) next-to-next-to-leading order. Key data sets
for the extraction of PDFs are provided by measurements
of inclusive deep-inelastic scattering (DIS) ℓN → ℓ′ X,
which is one of the two processes that we are considering in this work. Despite a lot of progress in the past
years, large uncertainties are still present for large values of the parton momentum fraction x [8]. As it turns
out, it is precisely this region that is particularly relevant
at the LHC, when trying to find signals of new physics
in, for example, (di-)jet measurements [9]. Furthermore,
the large-x region is also interesting as it can provide a
window into the non-perturbative dynamics of the color
confinement mechanism holding quarks and gluons inside
hadrons [10, 11].
On the experimental side, improvements for the gluon
PDF at large-x can be obtained from jet data taken at the
Tevatron and the LHC, direct photon production in fixed
target experiments, and from longitudinal DIS structure
functions. Concerning quark PDFs, the present focus
is mostly on low-energy experiments carried out for example at JLab [12], with important information coming
from directly reconstructed W charge asymmetries at the
Tevatron [8]. On the theoretical side a number of corrections to the pQCD calculations of these events are needed
in order to harvest fully the available and upcoming experimental data, and extract precise large-x quark and
gluon PDFs from global QCD fits. These corrections
include, in particular, resummation of threshold logarithms, Target Mass Corrections (TMCs), higher-twist
diagrams, and nuclear corrections when nuclear targets
are considered. The last three have been included consistently, for example, in the CTEQ-JLab collaboration
PDF fits [6] and the fits by Alekhin and collaborators
[13], allowing to substantially extend the range in x of
the fitted DIS data. Threshold resummation has been
considered in the past to estimate the theoretical errors
of PDFs or was used for fits of only a subset of the data
[14–16], but has not yet been fully included for all relevant data sets in a global QCD fit.
In the first part of this work, we consider the interplay
between two major corrections to the standard NLO formalism for DIS both of which have their greatest impact
at large-x, namely TMCs and higher order contributions
derived from threshold resummation. Here we choose
the collinear factorization TMC framework of Accardi
and Qiu [17], that contrary to most other approaches
[18] respects the kinematic xB ≤ 1 bound on the Bjorken
variable. Threshold resummation for QCD processes was
Maximal correlation between flavor entanglement and oscillation
damping due to localization effects
V. A. S. V. Bittencourt,∗ C. J. Villas Boas,† and A. E. Bernardini‡
Departamento de Física, Universidade Federal de São Carlos,
PO Box 676, 13565-905, São Carlos, SP, Brasil
arXiv:1411.3634v1 [hep-ph] 13 Nov 2014
(Dated: November 14, 2014)
Abstract
Localization effects and quantum decoherence driven by the mass-eigenstate wave packet propagation are shown to support a statistical correlation between quantum entanglement and damped
oscillations in the scenario of three-flavor quantum mixing for neutrinos. Once the mass-eigenstates
that support flavor oscillations are identified as three-qubit modes, a decoherence scale can be extracted from correlation quantifiers, namely the entanglement of formation and the logarithmic
negativity. Such a decoherence scale is compared with the coherence length of damped oscillations.
Damping signatures exhibited by flavor transition probabilities as an effective averaging of the oscillating terms are then explained as owing to loss of entanglement between mass modes involved
in the relativistic propagation.
PACS numbers: 03.65.Ta 03.65.Yz 03.67.-a 14.60.Pq
∗
Electronic address: [email protected]
†
Electronic address: [email protected]
‡
Electronic address: [email protected]
1
On the Validity of the Effective Field Theory for Dark
Matter Searches at the LHC
arXiv:1411.3600v1 [hep-ph] 13 Nov 2014
Giorgio Busoni∗
SISSA and INFN, Sezione di Trieste, via Bonomea 265, I-34136 Trieste, Italy
E-mail: [email protected]
Andrea De Simone
SISSA and INFN, Sezione di Trieste, via Bonomea 265, I-34136 Trieste, Italy
E-mail: [email protected]
Johanna Gramling
Section de Physique, Université de Genève,
24 quai E. Ansermet, CH-1211 Geneva, Switzerland
E-mail: [email protected]
Enrico Morgante
Section de Physique, Université de Genève,
24 quai E. Ansermet, CH-1211 Geneva, Switzerland
E-mail: [email protected]
Antonio Riotto
Section de Physique, Université de Genève,
24 quai E. Ansermet, CH-1211 Geneva, Switzerland
E-mail: [email protected]
We generalize in several directions our recent analysis of the limitations to the use of the effective
field theory approach to study dark matter at the LHC. Firstly, we study the full list of operators
connecting fermion DM to quarks and gluons, corresponding to integrating out a heavy mediator
in the s-channel; secondly, we provide analytical results for the validity of the EFT description
√
for both s = 8 TeV and 14 TeV; thirdly, we make use of a MonteCarlo event generator approach
to assess the validity of our analytical conclusions. We apply our results to revisit the current
collider bounds on the ultraviolet cut-off scale of the effective field theory and show that these
bounds are weakened once the validity conditions of the effective field theory are imposed.
XXII. International Workshop on Deep-Inelastic Scattering and Related Subjects,
28 April - 2 May 2014
Warsaw, Poland
∗ Speaker.
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Giorgio Busoni
EFT for Dark Matter Searched at LHC
1. Introduction
While there are many cosmological and astrophysical evidences that our universe contains a
sizable amount of dark Matter (DM), i.e. a component which clusters at small scales, its nature is
still a mystery. Currently, there are several ways to search for such DM candidates. DM particles
(if they are light enough) might reveal themselves in particle colliders, namely at the LHC. Many
LHC searches for DM are based on the idea of looking at events with missing energy plus a single
jet or photon, emitted from the initial state in pp collisions
pp → χ + χ + jet,
(1.1)
where χ indicates the DM particle. Several results are already available from two LHC collaborations [2–4]. In order to avoid the overwhelming model-dependence introduced by the plethora of
DM models discussed in the literature, DM searches at the LHC have made use of the Effective
Field Theory (EFT) [5, 6]. However, as far as collider searches are concerned, with the LHC being
such a powerful machine, it is not guaranteed that the events used to constrain an effective interaction are not occurring at an energy scale larger than the cutoff scale of the effective description.
The question about the validity of the EFT for collider searches of DM has become pressing (see
also Refs. [6, 7]), especially in the perspective of analysing the data from the future LHC run at
(13-14) TeV.
Let us consider a simple model where there is a heavy mediator of mass M, to which the quarks
and DM are coupled with couplings gq and gχ , respectively. The EFT is a good approximation
only at low energies. Indeed, it is possible at low energies to integrate out the heavy mediator
from the theory and obtain a tower of operators. The matching condition of the ultra-violet (UV)
√
theory with the mediator and its low-energy effective counterpart implies Λ = M/ gq gχ . A DM
production event occurs at an energy at which the EFT is reliable as long as Qtr < M, where Qtr
is the momentum transfer in the process; this, together with the condition of perturbativity of the
couplings gq,χ < 4π, implies
Qtr
Qtr
Λ> √
>
.
(1.2)
gq g χ
4π
It is clear that the details of condition (1.2) depend on the values of the couplings in the UV theory.
In the following, for definiteness, we will mostly identify the mass of the new degrees of freedom
M with the suppression scale of the operator Λ. This is equivalent to consider couplings in the UV
theory of O(1). So, we will deal with the condition (but we will discuss also the impact of taking
couplings larger than 1)
Qtr . Λ .
(1.3)
In Ref. [7] we have started the discussion of the limitations to the use of the EFT approach for
DM searches at the LHC by adopting a toy model where the heavy mediator is exchanged in the
s-channel and by introducing a few quantities which quantify the error made when using effective
operators to describe processes with very high momentum transfer. Our criteria indicated up to
what cutoff energy scale, and with what precision, the effective description is valid, depending on
the DM mass and couplings.
2
arXiv:1411.3587v1 [hep-ph] 13 Nov 2014
Preprint typeset in JHEP style - HYPER VERSION
CP3-14-72, ZU-TH 38/14
Two-loop splitting amplitudes and the single-real
contribution to inclusive Higgs production at N3LO
Claude Duhr
Center for Cosmology, Particle Physics and Phenomenology (CP3), Universit´e
Catholique de Louvain, Chemin du Cyclotron 2, B-1348 Louvain-La-Neuve, Belgium
Thomas Gehrmann, Matthieu Jaquier
Physik-Institut, Universit¨
at Z¨
urich, Wintherturerstrasse 190,
CH-8057 Z¨
urich, Switzerland
Abstract: The factorisation of QCD matrix elements in the limit of two external partons
becoming collinear is described by process-independent splitting amplitudes, which can
be expanded systematically in perturbation theory. Working in conventional dimensional
regularisation, we compute the two-loop splitting amplitudes for all simple collinear splitting processes, including subleading terms in the regularisation parameter. Our results are
then applied to derive an analytical expression for the two-loop single-real contribution to
inclusive Higgs boson production in gluon fusion to fourth order (N3 LO) in perturbative
QCD.
Keywords: QCD, N3LO, Higgs, LHC.
arXiv:1411.3586v1 [hep-ph] 13 Nov 2014
Preprint typeset in JHEP style - PAPER VERSION
Real-Virtual-Virtual contributions to the inclusive
Higgs cross section at N3LO
Falko Dulat
ETH Zurich, 8093 Zurich, Switzerland
E-mail: [email protected]
Bernhard Mistlberger
ETH Zurich, 8093 Zurich, Switzerland
E-mail: [email protected]
Abstract: We present the computation of the contributions to N3 LO inclusive Higgs
boson production due to two-loop amplitudes. Our result is a Laurent expansion in the
dimensional regulator, with coefficients that are linear combinations of harmonic polylogarithms of the ratio of the Higgs boson mass and the partonic center of mass energy. We
outline our method of solving the differential equations for master integrals appearing in
the cross section. Solving these differential equations requires the determination of boundary conditions and we present a new technique for decomposing the boundary conditions
into physical contributions. We show how these boundary conditions can be calculated
using the method of expansion by regions.
Keywords: Higgs, QCD, NNLO, N3LO, LHC and differential equations.
Preprint typeset in JHEP style - PAPER VERSION
arXiv:1411.3584v1 [hep-ph] 13 Nov 2014
CP3-14-71, ZU-TH 39/14, FERMILAB-PUB-14-461-T, NIKHEF 2014-048, CERN-PH-TH-2014-221
Higgs boson gluon-fusion production beyond threshold
in N3LO QCD
Charalampos Anastasioua , Claude Duhrb , Falko Dulata , Elisabetta Furlanc , Thomas
Gehrmannd , Franz Herzoge , Bernhard Mistlbergera
a
Institute for Theoretical Physics, ETH Z¨
urich, 8093 Z¨
urich, Switzerland
Center for Cosmology, Particle Physics and Phenomenology (CP3),
Universit´e catholique de Louvain,
Chemin du Cyclotron 2, 1348 Louvain-La-Neuve, Belgium
c
Fermilab, Batavia, IL 60510, USA
d
Physik-Institut, Universit¨
at Z¨
urich, Winterthurerstrasse 190, 8057 Z¨
urich, Switzerland
e
Nikhef, Science Park 105, NL-1098 XG Amsterdam, The Netherlands
CERN Theory Division, CH-1211, Geneva 23, Switzerland
b
Abstract: In this article, we compute the gluon fusion Higgs boson cross-section at N3 LO
through the second term in the threshold expansion. This calculation constitutes a major
milestone towards the full N3 LO cross section. Our result has the best formal accuracy
in the threshold expansion currently available, and includes contributions from collinear
regions besides subleading corrections from soft and hard regions, as well as certain logarithmically enhanced contributions for general kinematics. We use our results to perform
a critical appraisal of the validity of the threshold approximation at N3 LO in perturbative
QCD.
Keywords: Higgs physics, QCD, gluon fusion.
arXiv:1411.3563v1 [hep-ph] 13 Nov 2014
B → D ∗∗ – puzzle 1/2 vs 3/2
Benoˆıt Blossier
Laboratoire de Physique Th´eorique
CNRS/Universit´e Paris-Sud, Bˆat 210, F-91405 Orsay Cedex, FRANCE
Understanding the composition of final states in B → Xc lν could help to get a
feedback on the persisting disagreement between exclusive and inclusive determinations
of Vcb . In particular the series of orbital excitations D ∗∗ and radial excitations (D ′ , D ∗ ′ )
has received a lot of attention; a misinterpretation as a scalar state of the (D ′ → Dπ)
spectrum tail could have induced an experimental overestimate of the broad states
contribution to the total B → Xc lν width with respect to theoretical expectations,
all of them made however in the infinite mass limit: it is the so-called 1/2 vs 3/2
puzzle. We describe first attempts to measure on the lattice form factors of B →
D ∗∗ lν at realistic quark masses. Cleaner processes, like hadronic decays B → D ∗∗ π and
semileptonic decays Bs → Ds∗∗ lν in the strange sector have recently been examined by
phenomenologists, putting new interesting ideas on those issues with, again, the need of
lattice inputs.
PRESENTED AT
the 8th International Workshop on the CKM Unitarity Triangle (CKM
2014), Vienna, Austria, September 8-12, 2014
S: D
(∗)
P : D ∗∗
D±
D ∗±
D0∗
D1∗
D1
D2∗
Mass (MeV)
Width (MeV)
1869±0.5
2010±0.4
96±25
2352± 50
261 ± 50
2427± 26 ± 25 384+107
−75 ± 74
2421.8 ± 1.3
20.8+3.3
−2.8
2461.1± 1.6
32± 4
jlP
1−
2
1+
2
3+
2
JP
0−
1−
0+
1+
1+
2+
Table 1: Low-lying spectrum in the D sector; it is convenient to decompose the total orbital
momentum as J = 12 ⊕ jl , where jl is the orbital momentum of the light degrees of freedom.
1
Introduction
Understanding the long-distance dynamics of QCD is crucial in the control of the theoretical systematics on low-energy processes that are investigated at LHCb and, in the next years, at Super Belle,
to detect indirect effects of New Physics. It is particularly relevant for processes involving excited
states, that occur often in experiments. With that respect beauty and charmed mesons represent a
very rich sector. An intriguing question concerns the origin of the ∼ 3σ discrepancy between |Vcb|excl
and |Vcb |incl [1]: expressed differently, it is welcome to know more about the composition of the final
hadronic state Xc in the semileptonic decay B → Xc lν. We sketch in Table 1 the low-lying spectrum
+
+
of D mesons. The D states of the jlP = 12 doublet are broad while those of the jlP = 23 doublet
are narrow: indeed, the main decay channels are the non leptonic transitions D ∗∗ → D (∗) π. Parity
conservation implies that the pion has an even angular momentum ℓ with respect to D (∗) . Orbital
momentum conservation implies that ℓ = 0 or 2. That’s why D0∗ and D1∗ decay with a pion in the
S wave and D2∗ decays with the pion in the D wave. The decay D1 → D ∗ π occurs with the pion
in the S or D waves; however, thanks to Heavy Quark Symmetry, the latter is favored. Therefore,
+
+
decays of the jlP = 32 doublet are suppressed compared to decays of the 21 doublet. But Xc could
be made of radial excitations as well: the Babar Collaboration claimed to have isolated a bench of
new D states [2]. Among them, a structure in the D ∗ π distribution is interpreted as D(2550) ≡ D ′ .
After a fit, experimentalists obtain m(D ′ ) = 2539(8) MeV and Γ(D ′ ) = 130(18) MeV. A question
raised about the correctness of this interpretation because, in theory, quark models predict approximately the same D ′ mass (2.58 GeV) but a quite smaller width (70 MeV) [3]. However a well known
caveat is that excited states properties are very sensitive to the position of the wave functions nodes,
themselves depending strongly on the quark model. We collect in Table 2 the branching ratios of
the B → Xc semileptonic decays. We are interested by ∼ 25% of the total width Γ(B → Xc lν): 1/3
∗∗
of it comes from the channel B → Dnarrow
. Studying the channel B → D ′ lν, assuming it is quite
large [4] and using the fact that Γ(D ′ → D1/2 π) ≫ Γ(D ′ → D3/2 π), one concludes that an excess
of B → (D1/2 π)lν events could be observed with respect to their B → (D3/2 π)lν counterparts. A
question is then whether such a potentially large B → D ′ lν width could explain the ”1/2 vs. 3/2”
puzzle: [Γ(B → D1/2 lν) ≃ Γ(B → D3/2 lν)]exp while [Γ(B → D1/2 lν) ≪ Γ(B → D3/2 lν)]theory [5]. A
B→D1/2
τ1/2 (w) 2
2
. A detailed comkinematical factor explains partly this suppression: dΓB→D3/2 = (w+1)
2
τ3/2 (w)
dΓ
parison between theory and experiment is made in the center panel of Table 2. The main tension
1
TTP14-029
arXiv:1411.3549v1 [hep-ph] 13 Nov 2014
The double mass hierarchy pattern:
simultaneously understanding
quark and lepton mixing
Wolfgang Gregor Hollik∗
∗
1
and Ulises Jes´
us Salda˜
na Salazar∗,†
2
Institut f¨
ur Theoretische Teilchenphysik, Karlsruhe Institute of Technology
Engesserstraße 7, D-76131 Karlsruhe, Germany
†
Instituto de F´ısica, Universidad Nacional Aut´
onoma de M´exico
Apdo. Postal 20-364, 01000, M´exico D.F., M´exico
Abstract
The charged fermion masses of the three generations exhibit the two strong hierarchies m3 ≫ m2 ≫
m1 . We assume that also neutrino masses satisfy mν3 > mν2 > mν1 and derive the consequences of
the hierarchical spectra on the fermionic mixing patterns. The quark and lepton mixing matrices
are built in a general framework with their matrix elements expressed in terms of the four fermion
mass ratios mu /mc , mc /mt , md /ms , and ms /mb and me /mµ , mµ /mτ , mν1 /mν2 , and mν2 /mν3 ,
for the quark and lepton sector, respectively. In this framework, we show that the resulting mixing
matrices are consistent with data for both quarks and leptons, despite the large leptonic mixing
angles. The minimal assumption we take is the one of hierarchical masses and minimal flavour
symmetry breaking that strongly follows from phenomenology. No special structure of the mass
matrices has to be assumed that cannot be motivated by this minimal assumption. This analysis
allows us to predict the neutrino mass spectrum and set the mass of the lightest neutrino well below
0.01 eV. The method also gives the 1 σ allowed ranges for the leptonic mixing matrix elements.
Contrary to the common expectation, leptonic mixing angles are found to be determined solely by
the four leptonic mass ratios without any relation to symmetry considerations as commonly used in
flavor model building. Still, our formulae can be used to build up a flavor model that predicts the
observed hierarchies in the masses—the mixing follows then from the procedure which is developed
in this work.
1
2
E-mail: [email protected]
E-mail: [email protected]
Mixing of pseudoscalar-baryon and vector-baryon in the
J P = 1/2− sector and the N ∗ (1535) and N ∗(1650) resonances.
arXiv:1411.3547v1 [hep-ph] 13 Nov 2014
E. J. Garzon1 and E. Oset1
1
Departamento de F´ısica Te´orica and IFIC, Centro Mixto Universidad de
Valencia-CSIC, Institutos de Investigaci´on de Paterna, Aptdo. 22085, 46071 Valencia,
Spain
November 14, 2014
Abstract
We study the meson-baryon interaction with J P = 1/2− using the hidden-gauge Lagrangians
and mixing pseudoscalar meson-baryon with the vector meson-baryon states in a coupled channels
scheme with πN , ηN , KΛ, KΣ, ρN and π∆ (d-wave). We fit the subtraction constants of each
channel to the S11 partial wave amplitude of the πN scattering data extracted from experimental
data. We find two poles that we associate to the N ∗ (1535) and the N ∗ (1650) resonances and show
that the subtraction constants are all negative and of natural size. We calculate the branching ratios
for the different channels of each resonance and we find a good agreement with the experimental
data. The cross section for the π − p → ηn scattering is also evaluated and compared with experiment.
1
Introduction
Partial wave analyses of πN data [1, 2] have provided us with much data on amplitudes, cross sections and
resonance properties. It has also been the subject of intense theoretical investigations (see Refs. [3, 4] for
recent updates on the subject). The introduction of the chiral unitary techniques to study these reactions
in Ref. [5] resulted in surprising news that the N ∗ (1535) resonance was dynamically generated from the
interaction of meson baryon, with a price to pay: coupled channels had to be introduced. Some of the
channels were closed at certain energies, like the KΛ and KΣ in the region of the N ∗ (1535), but they were
shown to play a major role in the generation of this resonance, to the point of suggesting in Ref. [5] that
the N ∗ (1535) could qualify as a quasibound state of KΛ and KΣ. Work on this issue followed in Ref. [6],
corroborating the main findings of Ref. [5], and posteriorly in Refs. [7, 8, 9, 10]. In the chiral unitary
approach the loops of the Bethe-Salpeter equation must be regularized, and this is done with cut offs or
using dimensional regularization. The cut off, or equivalently the subtraction constants in dimensional
regularization in the different channels should be of “natural size”, as discussed in Ref. [10, 11, 12], if
one wishes to claim that the resonances have been generated dynamically from the interaction. However,
this is not the case of the N ∗ (1535), where different cut offs in Ref. [5], or different subtraction constants
in Ref. [6] for different channels must be used. This is unlike the case of the Λ(1405), where a unique
cut off in all channels leads to a good reproduction of the data [13, 11, 14, 15]. This fact was interpreted
in Ref. [10] as a manifestation of the nature of the two resonances, where the Λ(1405) would be largely
dynamically generated, while the N ∗ (1535) would contain a nonnegligible component of a genuine state,
formed with dynamics different from the pseudoscalar meson interaction. One might think of remnants
of an original seed of three constituent quarks, but this is not necessarily the case. It could also be due
to the missing of important channels different than pseudoscalar-baryon. Actually this has been a source
of investigation recently, where the mixing of pseudoscalar-baryon and vector-baryon channels has led
to interesting results and some surprises. In Ref. [16] the vector-baryon interaction was studied using
the method developed in Ref. [17] but mixing also pseudoscalar-baryon components. It was found that
the mixing produced a shift of some of the resonance positions of Ref. [17] and led to some increase
in the width. Similar results have been obtained recently in Refs. [18, 19, 20]. One of the interesting
1
Nuclear Physics B
Proceedings
Supplement
Nuclear Physics B Proceedings Supplement 00 (2014) 1–5
www.elsevier.com/locate/procedia
IFJPAN-IV-2014-15
arXiv:1411.3526v1 [hep-ph] 13 Nov 2014
Study of the tau meson decay modes with Monte Carlo
generator TAUOLA. Status and perspectives.
Olga Shekhovtsova
Institute of Nuclear Physics PAN ul. Radzikowskiego 152 31-342 Krakow, Poland
Kharkov Institute of Physics and Technology 61108, Akademicheskaya,1, Kharkov, Ukraine
Abstract
In the last two years substantial progress for the simulation of the process: τ− → π− π+ π− ντ by the Monte Carlo
generator TAUOLA was achieved. It is related to a new parametrization of the corresponding hadronic current based
on the Resonance Chiral Lagrangian and the recent availability of the unfolded distributions from the BaBar Collaboration analysis for all invariant hadronic masses. The theoretical model parameters were fitted to the one-dimensional
distributions provided by the BaBar Collaboration and results of the fit are discussed. A set of the hadronic currents for
other final states with two and three pseudoscalars is also installed in TAUOLA and the preliminary results for fitting
K + K − π− and π0 π− to BaBar and Belle data are presented.
c 2011 Published by Elsevier Ltd.
Keywords: Tau physics, Monte Carlo generator, TAUOLA, Resonance Chiral Lagrangian, Data analysis
1. Introduction
TAUOLA [1] is a Monte Carlo (MC) generator
dedicated to the generation of τ-lepton decays and
it is used in the analysis of experimental data both
at B-factories, BaBar [2] and Belle [3] Collaborations, and LHC [4]. The generator simulates more
than twenty decay modes, including both leptonic
and hadronic modes. The leptonic decay modes of
the τ lepton allow to test the universality of the lepton couplings to the gauge bosons. The hadronic
decays (in fact, the τ lepton due to its high mass is
the only one that can decay into hadrons) give information about the hadronization mechanism and
resonance dynamics in the energy region where the
Email address: [email protected]
(Olga Shekhovtsova)
methods of perturbative QCD cannot be applied.
Also hadronic flavour- and CP-violating decays of
the τ lepton allow to search for new physics scenarios. In addition, the tau lepton decay data allows us
to measure the Standard Model parameters, such
as the strong coupling constant, the quark-mixing
matrix, the strange quark mass etc.
The main problem in description of the hadronic
decay modes of the τ lepton is the lack of a theory coming from the first principle in the energy
region populated by the resonances (i.e. in the region of 1-2 GeV). The hadronic currents implemented in the first version of TAUOLA [1] as well
as in the internal versions of the code used by
BaBar and Belle are based on Vector Meson Dominance (VMD) approach. As shown in [5], Figs.
20.6.3 and 20.6.4, the current version of TAUOLA,
used by Belle collaboration does not give a sat-
Elastic Amplitudes and Observables in pp Scattering
A. Kendi Kohara, Erasmo Ferreira and Takeshi Kodama
arXiv:1411.3518v1 [hep-ph] 13 Nov 2014
Instituto de Física, Universidade Federal do Rio de Janeiro, C.P. 68528, Rio de Janeiro 21945-970, RJ, Brazil
Abstract.
Using a unified analytic representation for the elastic scattering
√amplitudes of pp scattering valid for all high energy region,
the behavior of observables in the LHC collisions in the range s = 2.76 - 14 TeV is discussed. Similarly to the case of 7
TeV data, the proposed amplitudes give excellent description of the preliminary 8 TeV data. We discuss the expected energy
dependence of the observable quantities, and present predictions for the experiments at 2.76, 13 and 14 TeV.
Keywords: <pp scattering ; hadronic collisions>
PACS: 13.85.-t,13.85.Lg,13.85.Tp,13.85.Dz
GENERAL INFORMATION AND DATA ANALYSIS
We establish explicitly disentangled real and imaginary amplitudes for pp elastic scattering based on a QCD motivated
model. With impact parameter representation (s,~b) and its Fourier transform in (s,~q) space both represented by simple
analytical forms, we are able to control unitarity and dispersion relation constraints, and provide geometric interpretation of the interaction range. The regularity obtained in the description of the data and the physical interpretation give
reliability to the proposed amplitudes.
The amplitudes of pp elastic scattering originally constructed through profile functions in b -space are written
αK −b2 /4βK
eK (γK (s), b) ,
TeK (s,~b) =
e
+ λK (s)ψ
2βK
with the usual Gaussian forms plus the characteristic shape functions
√2 2
√2 2 i
2eγK − γK +b /a0 h
eK (s, b) = q
ψ
1 − eγK − γK +b /a0 .
a0 γK2 + b2 /a0
(1)
(2)
The label K = R, I indicates either the real or the imaginary part of the complex amplitude.
For large b, corresponding to peripheral collisions, the amplitudes fall down with a Yukawa-like tail,
∼ (1/b) exp(−b/b0), that reflects effects of virtual partons (modified gluon field) at large distances in the Stochastic
Vacuum Model [1].
The comparison with d σ /dt data and determination of parameters are made with the amplitudes in t-space. The
quantities ΨK (γK (s),t = −~q2T ) obtained by Fourier transform of Eq. (1) are written
TKN (s,t) = αK (s)e−βK (s)|t| + λK (s)ΨK (γK (s),t) ,
and the shape functions converted to t− space take the form
√
−γK √1+a0 |t|
−γK 4+a0 |t| γK e
γK e
p
p
ΨK (γK (s),t) = 2 e
.
−e
1 + a0|t|
4 + a0|t|
(3)
(4)
The complete analysis of elastic scattering [2, 3, 4] requires also the contributions from the Coulomb interaction
at small |t| and from perturbative 3-gluon exchange at large |t|. The fixed parameter a0 = 1.39 GeV−2 is given by
the correlation length of the gluon condensate. All parameters have been determined as smooth functions of s and the
properties of the amplitudes (magnitudes, signs, zeros) have been described in detail [5].
In our normalization the elastic differential and the total cross sections are written
√
d σ I (s,t) d σ R (s,t)
d σ (s,t)
= (¯hc)2 [TI2 (s,t) + TR2 (s,t)] =
+
, σ (s) = (¯hc)2 4 π TIN (s,t = 0) .
dt
dt
dt
(5)
UCT-TP-301/2014
August 2014
arXiv:1411.3462v1 [hep-ph] 13 Nov 2014
Analytical determination of the QCD quark masses
1
C. A. Dominguez
Centre for Theoretical and Mathematical Physics and Department of Physics, University of Cape Town,
Rondebosch 7700, South Africa
Abstract
The current status of determinations of the QCD running quark masses is reviewed. Emphasis is on recent
progress on analytical precision determinations based on finite energy QCD sum rules. A critical discussion of
the merits of this approach over other alternative QCD sum rules is provided. Systematic uncertainties from
both the hadronic and the QCD sector have been recently identified and dealt with successfully, thus leading to
values of the quark masses with unprecedented accuracy. Results currently rival in precision with lattice QCD
determinations.
1
Introduction
Quark and gluon confinement in Quantum Chromodynamics (QCD) precludes direct experimental measurements of the fundamental QCD parameters, i.e. the strong interaction coupling and the quark masses. Hence,
in order to determine these parameters analytically one needs to relate them to experimentally measurable quantities. Alternatively, simulations of QCD on a lattice (LQCD) provide increasingly accurate numerical values
for these parameters, but little if any insight into their origin. The first approach relies on the intimate relation
between QCD Green functions, in particular their Operator Product Expansion (OPE) beyond perturbation
theory, and their hadronic counterparts. This relation follows from Cauchy’s theorem in the complex energy
plane, and is known as the finite energy QCD sum rule (FESR) technique [1]. In addition to producing numerical values for the QCD parameters, this method provides a detailed breakdown of the relative impact of the
various dynamical contributions. For instance, the strong coupling at the scale of the τ -lepton mass essentially
follows from the relation between the experimentally measured τ ratio, Rτ , and a contour integral involving
the perturbative QCD (PQCD) expression of the V + A correlator, a classic example of a FESR. This is the
cleanest, most transparent, and model independent determination of the strong coupling [2]-[3]. It also allows
to gauge the impact of each individual term in PQCD, up to the currently known five-loop order. Similarly,
in the case of the quark masses one considers a QCD correlation function which on the one hand involves the
quark masses and other QCD parameters, and on the other hand it involves a measurable (hadronic) spectral
function. Using Cauchy’s theorem to relate both representations, the quark masses become a function of QCD
parameters, e.g. the strong coupling, some vacuum condensates reflecting confinement, etc., and measurable
hadronic parameters. The virtue of this approach is that it provides a breakdown of each contribution to the
final value of the quark masses. More importantly, it allows to tune the relative weight of each of these contributions by introducing suitable integration kernels. This last feature has been used recently in the case of
1 To appear as a chapter in the book Fifty Years of Quarks, H. Fritzsch and M. Gell-Mann, editors (World Scientific Publishing
Company, Singapore).
1
Mass of Y (3940) in Bethe-Salpeter equation for quarks
Xiaozhao Chen1 and Xiaofu L¨
u2, 3, 4
1
Department of Foundational courses,
Shandong University of Science and Technology, Taian, 271019, China
arXiv:1411.3424v1 [hep-ph] 13 Nov 2014
2
3
Department of Physics, Sichuan University, Chengdu, 610064, China
Institute of Theoretical Physics, The Chinese Academy of Sciences, Beijing 100080, China
4
CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, China
(Dated: November 14, 2014)
Abstract
The general form of the Bethe-Salpeter wave functions for the bound states composed of two
vector fields of arbitrary spin and definite parity is corrected. Using the revised general formalism,
we investigate the observed Y (3940) state which is considered as a molecule state consisting of
¯ ∗0 . Though the attractive potential between D ∗0 and D
¯ ∗0 including one light meson (σ, π,
D ∗0 D
ω, ρ) exchange is considered, we find that in our approach the contribution from one-π exchange is
equal to zero and consider SU(3) symmetry breaking. The obtained mass of Y (3940) is consistent
with the experimental value.
PACS numbers: 12.40.Yx, 14.40.Rt, 12.39.Ki
1
Baryogenesis
A small review of the big picture
arXiv:1411.3398v1 [hep-ph] 12 Nov 2014
Csaba Bal´
azs, ARC Centre of Excellence for Particle Physics at the Tera-scale
School of Physics, Monash University, Melbourne, Victoria 3800, Australia
I schematically, and very lightly, review some ideas that fuel model building in the field of
baryogenesis. Due to limitations of space, and my expertise, this review is incomplete and
biased toward particle physics, especially supersymmetry.
To appear in the proceedings of the Interplay between Particle and Astroparticle Physics workshop,
18 – 22 August, 2014, held at Queen Mary University of London, UK.
1
Introduction
From the point of view of contemporary physics, the Universe is a strange place because
it contains a considerable amount of matter. We are so used to the existence of matter
around, or for that matter inside, us that we take it for granted. We are, however, hard
pressed to explain based on known fundamental principles why the Universe contains mostly
matter but hardly any antimatter. Our cardinal principles of the corpuscular world are
encapsulated in the Standard Model (SM) of elementary particles. This model contains
twelve types of matter particles: six quarks and six leptons. These matter particles are
differentiated by two quantum numbers: quarks carry a baryon number and leptons a unit
of lepton number. They all have antimatter partners. The mass, and all other quantum
numbers, of the anti-particles are the same as their partners’, with the exception of electric
charge, which is opposite.
Baryogenesis models attempt to understand the mechanism through which the cosmic
matter-antimatter asymmetry arises in the framework of elementary particle physics. They
offer mechanisms for creating matter-antimatter asymmetry from an initially symmetric
Universe [1]-[9].1 In a remarkable 1967 paper Sakharov established that baryogenesis requires three necessary ingredients [11]:
• baryon number (B) violation,
• violation of particle-antiparticle (C) symmetry, and the combined C and left-right or
parity (CP ) symmetry, and
• departure from thermal equilibrium.
These conditions are required components of all baryogenesis models.
1
In a similar vein leptogenesis models transfer an asymmetry created in the leptonic sector to todays
baryons [10].
1
arXiv:1411.3372v1 [hep-ph] 12 Nov 2014
International Journal of Modern Physics: Conference Series
c The Authors
A new approach to piecewise linear Wilson lines
Frederik F. Van der Veken
Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
[email protected]
Wilson lines are key objects in many QCD calculations. They are parallel transporters of
the gauge field that can be used to render non-local operator products gauge invariant,
which is especially useful for calculations concerning validation of factorization schemes
and in calculations for constructing or modelling parton density functions. We develop an
algorithm to express Wilson lines that are defined on piecewise linear paths in function
of their Wilson segments, reducing the number of diagrams needed to be calculated. We
show how different linear path topologies can be related using their color structure. This
framework allows one to easily switch results between different Wilson line structures,
which is helpful when testing different structures against each other, e.g. when checking
universality properties of non-perturbative objects.
Keywords: QCD; Wilson lines; TMDs.
PACS numbers: 11.15.Tk, 12.38.Aw, 12.38.Lg.
1. Introduction
A general Wilson line is an exponential of gauge fields along a path C, defined as:
U = P ei g
R
C
dz µ Aµ (z)
.
(1)
Because the gauge fields are non-Abelian, i.e. Aµ = ta Aaµ where ta is a generator of
a Lie algebra, they have to be path ordered, denoted by the symbol P in (1). The
fields are ordered such that the fields first on the path are written leftmost. After
making a Fourier transform, the path content is fully described by the following
integrals:
Z
n
Q
1
0
0
In =
P dλ1 · · · dλn (z1µ1 ) · · · (znµn ) ei ki ·zi ,
(2)
n!
so that the n-th order term of the Wilson line expansion is given by
Z ω
dω kn
d k1
n
·
·
·
Un = (ig)
ω
ω Aµn (−kn )· · ·Aµ1 (−k1 ) In .
(2π)
(2π)
(3)
This is an Open Access article published by World Scientific Publishing Company. It is distributed
under the terms of the Creative Commons Attribution 3.0 (CC-BY) License. Further distribution
of this work is permitted, provided the original work is properly cited.
1
arXiv:1411.3353v1 [hep-ph] 12 Nov 2014
Complementarity between collider, direct detection,
and indirect detection experiments
Matthew Cahill-Rowley∗†
SLAC, USA
E-mail: [email protected]
We examine the capabilities of planned direct detection, indirect detection, and collider experiments in exploring the 19-parameter p(henomenological)MSSM, focusing on the complementarity between the different search techniques. In particular, we consider dark matter searches at
the 7, 8 (and eventually 14) TeV LHC, Fermi, CTA, IceCube/DeepCore, and LZ. We see that
the search sensitivities depend strongly on the WIMP mass and annihilation mechanism, with the
result that different search techniques explore orthogonal territory. We also show that advances in
each technique are necessary to fully explore the space of Supersymmetric WIMPs.
Science with the New Generation of High Energy Gamma-ray experiments, 10th Workshop
04-06 June 2014
Lisbon - Portugal
∗ Speaker.
†A
footnote may follow.
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Complementarity between collider, direct detection, and indirect detection experiments
Matthew Cahill-Rowley
1. Introduction
Determining the identity of dark matter (DM) is one of the most pressing issues before us
today. One promising class of dark matter candidates is Weakly Interacting Massive Particles
(WIMPs), which predict the observed relic abundance through the simple mechanism of thermal
freeze-out. WIMPs naturally appear in many extensions of the Standard Model (SM) that resolve
the gauge hierarchy, with the most notable example being supersymmetry (SUSY). Several important classes of experimental techniques have been proposed to detect non-gravitational signatures
of WIMP DM. These techniques include direct detection of WIMPs scattering off of nuclei, indirect detection of WIMPs by observing excesses of high-energy SM particles resulting from WIMP
annihilation, and direct production of WIMPs in high energy colliders. In this paper, we seek to
understand how these different techniques complement each other within the framework of the
phenomenological Minimal Supersymmetric Standard Model (pMSSM). We find that the three
techniques place orthogonal constraints on the parameter space and that advances in all three techniques are necessary to cover the supersymmetric WIMP sector. This paper presents results from
the study described in [1]. In particular, detailed descriptions of the pMSSM and the constraints
we apply can be found in that document and the references contained therein.
It is well-known that R-parity conserving supersymmetry predicts a stable dark matter candidate in the form of the lightest SUSY particle (LSP). Cosmological observations require the LSP
to have no electric or color charge. Models with the lightest neutralino, χ10 , as the LSP satisfy
these requirements and will be the focus of this study. The DM phenomenology of these models
is determined not only by the composition of the LSP (whether it is mostly comprised of the superpartners of the U(1) or SU(2) gauge bosons or the neutral Higgses), but also in general on the
other SUSY particles, which can alter the annihilation and scattering rates and are important for the
model’s discovery potential at the LHC. Unfortunately, the simplest SUSY scenario, the MSSM,
has (∼100) parameters, making it far too large to explore in full generality. However, many of these
parameters are restricted by the non-observation of large flavor violating effects. This allows us to
simplify the parameter space by imposing the following experimentally-motivated assumptions: (i)
no new phase appearing in the soft-breaking parameters, i.e., CP conservation, (ii) Minimal Flavor
Violation at the electroweak scale such that the CKM matrix drives flavor mixing, (iii) degenerate
first and second generation soft sfermion masses, and (iv) negligible Yukawa couplings and associated A-terms for the first two generations. These assumptions reduce the original space down
to the 19-parameter pMSSM. We emphasize that no assumption about high-scale physics, such
as the mechanism of SUSY breaking or unification of sparticle masses, has been applied to produce the pMSSM, and that it is therefore an “unprejudiced” approach to understanding TeV-scale
supersymmetry.
Despite these simplifications, 19 parameters is too large for a systematic grid approach. We
therefore perform a random sample of the pMSSM, testing 3 million points against experimental
and theoretical constraints. The result is 223256 parameter space points (which we will call “models”) satisfying all pre-LHC experimental constraints. Note that only about 20% of the models
predict the correct Higgs mass within the calculational uncertainty. However, we have found the
LHC and DM constraints to be essentially dependent of mh for the range of Higgs masses in our
model set. We assume that the LSP has its thermal relic abundance (calculated using micrOMEGAs
2
Probing short-lived fluctuations in hadrons and nuclei
Stéphane Munier
arXiv:1411.3349v1 [hep-ph] 12 Nov 2014
Centre de physique théorique, École Polytechnique, CNRS, Palaiseau, France
Abstract. We develop a picture of dipole-nucleus (namely dilute-dense) and dipole-dipole (dilute-dilute) scattering in the
high-energy regime based on the analysis of the fluctuations in the quantum evolution. We emphasize the difference in
the nature of the fluctuations probed in these two processes respectively, which, interestingly enough, leads to observable
differences in the scattering amplitude profiles.
Keywords: Quantum chromodynamics, high-energy scattering, hadronic cross sections, parton evolution, color dipole model, fluctuations
PACS: 12.38.-t,13.85.-t
This paper introduces and summarizes the results recently published in Ref. [1], from a less technical viewpoint (see
Ref. [2] for a complementary presentation), and with illustrations from numerical simulations (see Figs. 2 and 3 below).
Our goal is to understand the qualitative properties of the short-lived and short-distance (with respect to 1/ΛQCD )
quantum fluctuations, namely the ones that are probed most efficiently in deep-inelastic scattering experiments in the
small-xBj regime, or in observables in proton-proton and proton-nucleus scattering whose cross sections may be related
to dipole amplitudes (see e.g. Ref. [3]). (A recent general review of high-energy QCD can be found in Ref. [4]).
We shall first describe qualitatively the scattering of two color dipoles and of a dipole off a nucleus, before turning
to an analysis of the quantum fluctuations. We shall eventually review the most striking quantitative prediction derived
from our discussion.
Our picture relies on the well-known color dipole model [5], which describes, in the framework of perturbative
quantum chromodynamics, how the quantum state of a hadron builds up from a cascade of dipole splittings.
PICTURE OF THE INTERACTION OF A SMALL DIPOLE WITH QCD MATTER
Scattering of a dipole off a dilute target and off a dense target
We start with the scattering of two color dipoles (concretely, e.g. two quark-antiquark pairs) of respective transverse
sizes r0 and R0 with the ordering |r0 | < |R0 |.
At low energy, the forward elastic scattering amplitude of the dipoles consists in the exchange of a pair of gluons.
Since the dipoles are colorless, this exchange can take place only if their sizes are comparable (on a logarithmic scale),
and if the scattering occurs at coinciding impact parameters. Once these conditions are fulfilled, the cross section is
parametrically proportional to αs2 .
√
Let us go to larger center-of-mass energies s by boosting the small dipole to the rapidity y = ln(sR20 ). The most
probable Fock state at the time of the interaction is then a dense state of gluons, which may be represented by a
set of dipoles [5] (see the sketch in Fig. 1a). The amplitude is now enhanced by the number of these dipoles which
have a size of the order of R0 . We may define a “one-event amplitude” Tdone event , which is related to the probability
that gluons are exchanged between one given realization of the dipole evolution and the target dipole. If n(r0 , r|y)
denotes the number of dipoles in a given realization of the evolution up to rapidity y of size r, starting with a dipole
of size r0 , then Tdone event (r0 , R0 |y) ≃ αs2 × n(r0 , R0 |y), where it is understood that the impact parameters of the dipoles
which scatter need to coincide (up to a distance of order of the smallest size). Of course, the dipole number fluctuates
from event to event, and so does Tdone event . The physical amplitude measured in an experiment is proportional to the
average of the latter over events, namely over realizations of the dipole evolution. We conclude that the scattering of
two dipoles of respective sizes r0 and R0 probes the density of gluons of transverse size R0 , at a given impact parameter, in typical quantum fluctuations of a source dipole of size r0 appearing in the quantum evolution over the rapidity y.
We turn to the case in which instead of the dipole of size R0 , the target consists in a large nucleus. At low
UCB-PTH-14/38, UWThPh-2014-27
Prepared for submission to JHEP
arXiv:1411.3342v1 [hep-ph] 12 Nov 2014
Connecting Dark Matter UV Complete Models to
Direct Detection Rates via Effective Field Theory
Francesco D’Eramoa,b and Massimiliano Procurac,d
a
Department of Physics, University of California, Berkeley, CA 94720, USA
Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
c
Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics,
University of Bern, CH-3012 Bern, Switzerland
d
Fakultät für Physik, Universität Wien, Boltzmanngasse 5, 1090 Vienna, Austria
b
E-mail: [email protected], [email protected]
Abstract: Direct searches for WIMPs are sensitive to physics well below the weak scale.
In the absence of light mediators, it is fruitful to apply an Effective Field Theory (EFT)
approach accounting only for dark matter (DM) interactions with Standard Model (SM)
fields. We consider a singlet fermion WIMP and effective operators up to dimension 6
which are generated at the mass scale of particles mediating DM interactions with the SM.
We perform a one-loop Renormalization Group Evolution (RGE) analysis, evolving these
effective operators from the mediators mass scale to the nuclear scales probed by direct
searches. We apply our results to models with DM velocity-suppressed interactions, DM
couplings only to heavy quarks, leptophilic DM and Higgs portal, which without our analysis
would not get constrained from direct detection bounds. Remarkably, a large parameter
space region for these models is found to be excluded as a consequence of spin-independent
couplings induced by SM loops. In addition to these examples, we stress that more general
renormalizable models for singlet fermion WIMP can be matched onto our EFT framework,
and the subsequent model-independent RGE can be used to compute direct detection rates.
Our results allow us to properly connect the different energy scales involved in constraining
WIMP models, and to combine information from direct detection with other complementary
searches, such as collider and indirect detection.
Anomalous solutions to the strong CP problem
Anson Hook1
arXiv:1411.3325v1 [hep-ph] 12 Nov 2014
1
School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540, USA
We present a new mechanism for solving the strong CP problem using a Z2 discrete symmetry and
an anomalous U (1) symmetry. A Z2 symmetry is used so that two gauge groups have the same theta
angle. An anomalous U (1) symmetry makes the difference between the two theta angles physical
and the sum unphysical. Two models are presented where the anomalous symmetry manifests itself
in the IR in different ways. In the first model there are massless bifundamental quarks, a solution
reminiscent of the massless up quark solution. In the IR of this model, the η 0 boson relaxes the QCD
theta angle to the difference between the two theta angles - in this case zero. In the second model,
the anomalous U (1) symmetry is realized in the IR as a dynamically generated mass term that
has exactly the phase needed to cancel the theta angle. Both of these models make the extremely
concrete prediction that there exist new colored particles at the TeV scale.
The smallness of QCD’s θ angle has been a mystery
for many years. The physically observable angle is
θ = θ + arg detYu Yd
(1)
where θ is the theta angle and Yu,d are the up and down
type yukawas respectively. Measurements show that θ
must be smaller than 10−10 [1]. This result is especially
surprising considering that the CP violating phase in the
CKM matrix is order one. As both CP violating phases
have contributions from the yukawa matrices, it is surprising that one should be large while the other is so
small. This difference is a fine tuning of ten orders of
magnitude and begs a dynamical explanation.
There are two broad categories for solutions to the
strong CP problem. The first type are solutions based
on the CP and P discrete symmetries. The solutions
which use the CP symmetry start with a CP invariant
theory and spontaneously break it in such a way that the
theta angle vanishes at tree level while the CKM phase is
large. The most well known of these types of theories is
the Nelson-Barr mechanism [2, 3]. Other solutions based
off of P involve doubling the matter content of the SM
such that the opposite parity sector carries the opposite
theta angle[4]. Diagonal subgroups thus have non-zero
CKM phases but vanishing θ.
The second class of solutions are based off of anomalous symmetries. The idea behind these solutions is that
in the UV there exists an anomalous symmetry which
can be used to rotate away the theta angle and render it
unphysical. These solutions are differentiated from each
other by how the anomalous symmetry is realized in the
IR. One popular IR realization of the anomalous symmetry is the axion [5–8]. In the axion solution to the
strong CP problem, an anomalous symmetry is spontaneously broken yielding a pseudo goldstone boson, the
axion. QCD dynamics generate a potential for the axion. At the minimum of the potential, the axion vev
cancels θ.
Another solution to the strong CP problem that uses
an anomalous symmetry is the massless up quark solution [9], which is currently disfavored by data [10]. In
the presence of a massless up quark, a chiral rotation of
the up quark can remove θ without changing any physical parameters of the theory. θ is thus an unobservable
parameter. After confinement, there should be another
dual description of how θ is removed. This dual description is accomplished by the η 0 boson. In the large N limit,
the η 0 boson has a small mass and can be incorporated
into the low energy effective field theory of the goldstone
bosons. The low energy effective description for the η 0
gauge boson[11] is
L = fπ2 Tr∂µ Σ∂ µ Σ† + afπ3 Tr mΣ + m† Σ†
(2)
2
i
+bfπ4 θ + (Tr log Σ − Tr log Σ† ) + · · ·
2
where a is O(1), b is O(1/N ) and m is the mass of the
quarks. Σ is the non-linear sigma field describing the
breaking of U (3)L × U (3)R down to the diagonal, i.e. it
contains the η 0 boson in addition to the usual pions. The
η 0 vev is stabilized around the theta angle. All additional
higher dimensional operators are a function of η 0 − θfπ
as required by the anomalous symmetry. Thus once η 0 is
integrated out, the only place in the Lagrangian where
θ appears is in the mass terms. If the mass is zero then
the entire IR Lagrangian is independent of θ. This is the
IR description of the massless up quark solution to the
strong CP problem.
In the absence of an up quark mass, the η 0 boson has
a shift symmetry that relaxes the θ angle to 0. The difference between the massless up quark solution and the
axion solution is that the observed η 0 boson obeys
mη0 , fη0 ≈ ΛQCD
while the unobserved axion typically has
√
mu md
ma fa = fπ mπ
mu + md
(3)
(4)
Both of these solutions are realized in the IR as scalars
with a shift symmetry that renders theta unphysical.
In this work, we consider a using a Z2 discrete symmetry in conjunction with an anomalous symmetry to
Emergent soft monopole modes in weakly-bound deformed nuclei
J.C. Pei,1 M. Kortelainen,2, 3 Y.N. Zhang,1 and F.R. Xu1
arXiv:1411.3418v1 [nucl-th] 13 Nov 2014
1
State Key Laboratory of Nuclear Physics and Technology,
School of Physics, Peking University, Beijing 100871, China
2
Department of Physics, P.O. Box 35 (YFL), University of Jyv¨
askyl¨
a, FI-40014 Jyv¨
askyl¨
a, Finland
3
Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland
Based on the Hartree-Fock-Bogoliubov solutions in large deformed coordinate spaces, the finite
amplitude method for quasiparticle random phase approximation (FAM-QRPA) has been implemented, providing a suitable approach to probe collective excitations of weakly-bound nuclei embedded in the continuum. The monopole excitation modes in Magnesium isotopes up to the neutron
drip line have been studied with the FAM-QRPA framework on both the coordinate-space and harmonic oscillator basis methods. Enhanced soft monopole strengths and collectivity as a result of
weak-binding effects have been unambiguously demonstrated.
PACS numbers: 21.10.Gv, 21.10.Re, 21.60.Jz
Nuclei close to the particle drip lines are weakly
bound superfluid quantum systems and can exhibit exotic threshold phenomena [1], sharing interdisciplinary
interests with weakly bound systems such as multi-quark
states, Rydberg atoms and quantum droplets [1–3]. Since
the discovery of nuclear halos with radioactive beams [4],
there have been numerous theoretical developments aiming at weakly-bound nuclei and their dilute surfaces [5].
Extensive Hartree-Fock-Bogoliubov (HFB) studies have
provided successful descriptions of continuum couplings
and halo features in ground states of weakly-bound nuclei [6–12]. On the other hand, excitations in weaklybound nuclei opened vast possibilities to probe novel collective modes, as well as continuum effects and components of the effective interaction that are suppressed in
ground states [13–15]. To address these issues, along with
forthcoming facilities such as FRIB, an accurate and selfconsistent treatment of continuum together with pairing
correlations, deformations and large spatial extensions is
essential.
Among the excited states in weakly-bound nuclei, the
emergent soft excitation modes (or pygmy resonances)
which correspond to the collective motion between neutron halo/skins and cores, are particularly intriguing.
These modes can impact astrophysical neutron capture
rates and r-process nucleosynthesis. However, the collectivity of observed pygmy resonances, as a crucial verification of coherence, is still under debate [13, 14, 16].
This Rapid Communication is devoted to the low-energy
monopole excitations in weakly-bound nuclei, caused due
to the soft incompressibility of halos, as the dilute nuclear matter has a decreased incompressibility compared
to saturated densities [17]. The low-energy monopole
modes indeed have been predicted, e.g., in the neutronrich Nickel isotopes (observed very recently in 68 Ni [18]),
as a rather non-collective excitation [19]; however, it
may hardly be expected in another RPA calculation
with a proper treatment of continuum [20]. Besides, the
collectivity could be enhanced due to weak-binding effects [15]. Therefore, the emergence of collective soft
monopole modes, as well as the role of continuum con-
tributions with the fully self-consistent continuum quasiparticle random phase approximation (QRPA) approach,
is still an open question.
The standard method to solve the QRPA equation as
a matrix form involves tremendous computational costs
in deformed cases, and even more when continuum configurations are included [21]. Recently, the developments
of the Finite Amplitude Method (FAM), by Nakatsukasa
et. al., provided an alternative way to solve the QRPA
problem iteratively [22, 23] rather than by a direct matrix
diagonalization. The FAM-QRPA method provides an efficient way to study collective excitations and it has been
implemented on several HFB approaches, such as the
spherical coordinate-space HFB [23], deformed harmonic
oscillator (HO) and transformed HO basis HFB [25], and
deformed relativistic Hartree-Bogoliubov method [24].
Recently, FAM-QRPA method has been also applied to
the discrete modes [26] and β-decays [27].
In this Rapid Communication, we have developed a
FAM-QRPA approach based on HFB solutions in large,
axially symmetric coordinate-spaces, to describe excitations in weakly-bound deformed nuclei, which was a great
computationally challenge. In deformed weakly-bound
nuclei, the subtle interplay among surface deformations,
surface diffuseness, and continuum couplings can result in
exotic structures, such as deformed halos. Therefore theoretical studies of ground state properties and excitations
need precise HFB solutions to account these phenomena.
The conventional HFB approach, based on the HO basis
may not be sufficient to describe the surface properties
of weakly bound systems. On the other hand, the exact treatment of the continuum in deformed cases, with
scattering boundary conditions, is rarely employed [10].
In this context, the HFB approach in large deformed
coordinate-spaces can provide very precise descriptions of
ground states in deformed weakly-bound nuclei, including quasiparticle resonances and dense continuum spectra, and this has been accomplished recently with a hybrid parallel calculation scheme [12]. Therefore, the next
natural step is to combine the FAM-QRPA method with
the deformed large coordinate-space HFB approach, to
SNSN-323-63
November 14, 2014
arXiv:1411.3687v1 [nucl-ex] 13 Nov 2014
The Neutron Lifetime
F. E. Wietfeldt1
Department of Physics and Engineering Physics
Tulane University, New Orleans, LA 70118 USA
The decay of the free neutron into a proton, electron, and antineutrino is the prototype semileptonic weak decay and the simplest example
of nuclear beta decay. The nucleon vector and axial vector weak coupling constants GV and GA determine the neutron lifetime as well as
the strengths of weak interaction processes involving free neutrons and
protons that are important in astrophysics, cosmology, solar physics and
neutrino detection. In combination with a neutron decay angular correlation measurement, the neutron lifetime can be used to determine the
first element of the CKM matrix Vud . Unfortunately the two main experimental methods for measuring the neutron lifetime currently disagree
by almost 4σ. I will present a brief review of the status of the neutron
lifetime and prospects for the future.
PRESENTED AT
The 8th International Workshop on the CKM Unitarity
Triangle (CKM 2014)
Vienna, Austria September 8–12, 2014
1
Work supported by the U.S. National Science Foundation grant PHY-1205266
A free neutron decays into a proton, electron, and antineutrino with a lifetime of
about 880 s. This semileptonic weak decay occurs because the neutron mass is slightly
larger than that of the final state system. Because the mass difference and hence the
decay energy 1.29 MeV is so small, the details of this interaction at the quark level are
unimportant and the process can be effectively treated as a four-fermion interaction
with the matrix element:
M = [GV p γµ n − GA p γ5 γµ n] [e γµ (1 + γ5 ) ν] .
(1)
The nucleon vector and axial vector effective weak coupling constants GV and GA
determine the neutron decay rate and therefore the neutron lifetime:
τn =
2π 3h
¯7
m5e c4 fR
!
1
G2V + 3G2A
(2)
where fR is a phase space factor that includes final state and radiative corrections.
Conservation of vector current (CVC) requires that the vector weak coupling in the
nucleon system has the same strength as for a bare quark, i.e. GV = GF Vud , where
GF is the universal weak coupling constant obtained most precisely from the muon
lifetime: GF = 1.1663787(6) × 10−5 GeV−2 [1], and Vud is the first element of the
CKM matrix. Axial current is not conserved so the value of GA is altered by the
strong interaction in the hadronic environment. Thus GA = GF Vud λ, where λ is
measured experimentally from neutron decay. A measurement of the neutron lifetime
τn along with λ (via a neutron decay angular correlation measurement such as the
beta asymmetry [2]) determines GA , GV , and using the known value of GF , Vud . This
relationship, via Eq. 2, can be expressed in the following convenient form [3]:
|Vud |2 =
4908.7(1.9)s
τn (1 + 3λ2 )
(3)
Currently the most precise determinations of both GV and Vud come from the F t
values of 13 superallowed 0+ → 0+ beta decay systems yielding Vud = 0.97425(22)
[4, 5, 6], a precision of 2 × 10−4 , limited by theoretical uncertainties in the radiative,
isospin breaking, and nuclear structure corrections. The neutron decay determination of Vud is, in principle, preferred as it is free of isospin breaking and nuclear
structure corrections. The problem is the relatively worse precision and consistency
in experimental results for λ and τn .
After the Big Bang, neutrons and protons were in thermal equilibrium via semileptonic weak interactions until the universe expanded to where the lepton density and
temperature were too low to maintain equilibrium. This is called nucleon “freeze
out”, at about t = 1 s. The ratio of neutrons to protons was then fixed by a Boltzmann factor: n/p = exp(−∆m/kTfreeze ) ≈ 61 . The neutron lifetime directly provides
the combination G2V + 3G2A that determines the semileptonic weak interaction rate
1