1. No category

arXiv:1411.1433v1 [physics.ins-det] 5 Nov 2014
Preprint typeset in JINST style - HYPER VERSION
Radiopurity assessment of the tracking readout for
the NEXT double beta decay experiment
V. Álvarez,a I. Bandac,b A.I. Barrado,c A. Bettini,b,d F.I.G.M. Borges,e M. Camargo, f
S. Cárcel,a S. Cebrián,b,g∗A. Cervera,a C.A.N. Conde,e E. Conde,c T. Dafni,b,g J. Díaz,a
R. Esteve,h L.M.P. Fernandes,e M. Fernández,h P. Ferrario,a A.L. Ferreira,i
E.D.C. Freitas,e V.M. Gehman,i A. Goldschmidt,i H. Gómez,b,g J.J. Gómez-Cadenas,a†
D. González-Díaz,b,g R.M. Gutiérrez, f J. Hauptman,k J.A. Hernando Morata,l
D.C. Herrera,b,g F.J. Iguaz,b,g I.G. Irastorza,b,g L. Labarga,m A. Laing,a I. Liubarsky,a
D. Lorca,a M. Losada, f G. Luzón,b,g A. Marí,h J. Martín-Alboa A. Martínez,a
G. Martínez-Lema,l T. Miller,i F. Monrabal,a M. Monserrate,a C.M.B. Monteiro,e
F.J. Mora,h L.M. Moutinho,i J. Muñoz Vidal,a M. Nebot-Guinot,a D. Nygren,i
C.A.B. Oliveira,i A. Ortiz de Solórzano,b,g J. Pérez,n J.L. Pérez Aparicio,o J. Renner,i
L. Ripoll, p A. Rodríguez,b,g J. Rodríguez,a F.P. Santos,e J.M.F. dos Santos,e
L. Segui,b,g L. Serra,a D. Shuman,i A. Simón,a C. Sofka,q M. Sorel,a J.F. Toledo,h
J. Torrent, p Z. Tsamalaidze,r J.F.C.A. Veloso,i J.A. Villar,b,g R.C. Webb,q J.T. White,q
N. Yahlalia
–1–
A BSTRACT: The “Neutrino Experiment with a Xenon Time-Projection Chamber” (NEXT) is intended to investigate the neutrinoless double beta decay of 136 Xe, which requires a severe suppression of potential backgrounds; therefore, an extensive screening and selection process is underway to control the radiopurity levels of the materials to be used in the experimental set-up of
NEXT. The detector design combines the measurement of the topological signature of the event for
background discrimination with the energy resolution optimization. Separate energy and tracking
readout planes are based on different sensors: photomultiplier tubes for calorimetry and silicon
multi-pixel photon counters for tracking. The design of a radiopure tracking plane, in direct contact with the gas detector medium, was a challenge since the needed components have typically
activities too large for experiments requiring ultra-low background conditions. Here, the radiopurity assessment of tracking readout components based on gamma-ray spectroscopy using ultra-low
background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain) is described.
According to the obtained results, radiopure enough printed circuit boards made of kapton and
copper and silicon photomultipliers, fulfilling the requirements of an overall background level in
that region of at most 8 × 10−4 counts keV−1 kg−1 y−1 , have been identified.
K EYWORDS : Double beta decay; Time-Projection Chamber (TPC); Gamma detectors (HPGe);
Search for radioactive material.
∗ Corresponding
† Spokesperson
author ([email protected]).
([email protected]).
Theoretical Constraints and Systematic Effects in the Determination of the Proton Form
Factors
I. T. Lorenz,1, ∗ Ulf-G. Meißner,1, 2, † H.-W. Hammer,3, 4 and Y.-B. Dong5, 6
1
Helmholtz-Institut f¨ur Strahlen- und Kernphysik and Bethe Center for Theoretical Physics,
Universit¨at Bonn, D–53115 Bonn, Germany
arXiv:1411.1704v1 [hep-ph] 6 Nov 2014
2
Institute for Advanced Simulation, Institut f¨ur Kernphysik and J¨ulich Center for Hadron Physics,
Forschungszentrum J¨ulich, D–52425 J¨ulich, Germany
3
Institut f¨ur Kernphysik, Technische Universit¨at Darmstadt, 64289 Darmstadt, Germany
4
ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum f¨ur
Schwerionenforschung GmbH, 64291 Darmstadt, Germany
5
6
Institute of High Energy Physics, Beijing 100049, P. R. China
Theoretical Physics Center for Science Facilities (TPCSF), CAS, Beijing 100049, P. R. China
We calculate the two-photon exchange corrections to electron-proton scattering with nucleon and ∆
intermediate states. The results show a dependence on the elastic nucleon and nucleon-∆-transition
form factors used as input which leads to significant changes compared to previous calculations. We
discuss the relevance of these corrections and apply them to the most recent and precise data set
and world data from electron-proton scattering. Using this, we show how the form factor extraction
from these data is influenced by the subsequent inclusion of physical constraints. The determination
of the proton charge radius from scattering data is shown to be dominated by the enforcement of a
realistic spectral function. Additionally, the third Zemach moment from the resulting form factors
is calculated. The obtained radius and Zemach moment are shown to be consistent with Lamb shift
measurements in muonic hydrogen.
Contents
I. Introduction
II. Form factor extraction and corrections
∗
†
2
4
A. Definitions of form factors and helicity amplitudes
4
B. Two-photon exchange corrections
6
C. Results on two-photon-exchange calculations
8
Electronic address: [email protected]
Electronic address: [email protected]
EPJ manuscript No.
(will be inserted by the editor)
Unquenched quark-model calculation of X(3872)
electromagnetic decays
Marco Cardoso1 , George Rupp2 , and Eef van Beveren3
1
2
arXiv:1411.1654v1 [hep-ph] 6 Nov 2014
3
Centro de F´ısica Te´
orica de Part´ıculas, Instituto Superior T´ecnico, Universidade de Lisboa, P-1049-001 Lisbon, Portugal
Centro de F´ısica das Interac¸co
˜es Fundamentais, Instituto Superior T´ecnico, Universidade de Lisboa, P-1049-001 Lisbon,
Portugal
Centro de F´ısica Computacional, Departamento de F´ısica, Universidade de Coimbra, P-3004-516 Coimbra, Portugal
Received: date / Revised version: date
Abstract. A recent quark-model description of X(3872) as an unquenched 2 3P1 c¯
c state is generalised
by now including all relevant meson-meson configurations, in order to calculate the widths of the experimentally observed electromagnetic decays X(3872) → γJ/ψ and X(3872) → γψ(2S). Interestingly, the
inclusion of additional two-meson channels, most importantly D± D?∓ , leads to a sizeable increase of the
¯ ?0 component remains the dominant one.
c¯
c probability in the total wave function, although the D0 D
As for the electromagnetic decays, unquenching strongly reduces the γψ(2S) decay rate yet even more
sharply enhances the γJ/ψ rate, resulting in a decay ratio compatible with one experimental observation but in slight disagreement with two others. Nevertheless, the results show a dramatic improvement
as compared to a quenched calculation with the same confinement force and parameters. Concretely, we
obtain Γ (X(3872) → γψ(2S)) = 28.9 keV and Γ (X(3872) → γJ/ψ) = 24.7 keV, with branching ratio
Rγψ = 1.17.
1 Introduction
tetraquark or molecular approaches. On the other hand,
the latter paper [6] focused on the X(3872) wave function,
Since its discovery [1] by the Belle Collaboration in 2003, using instead a coordinate-space model and with only two
c and D0 D?0 . The purpose was to study
the very narrow axial-vector [2] charmonium state X(3872) channels, viz. c¯
whether
the
charm-anticharm
component would remain
has become one of the favourite theoretical laboratories for
meson spectroscopists, because of its remarkable closeness substantial, despite the very long tail of the D0 D?0 com¯ ?0 (or D
¯ 0 D?0 ) and ρ0 J/ψ thresholds, besides ponent due to the small binding of less than 0.2 MeV [2].
to the D0 D
c probability of about 7.5% was found and —
its seemingly too low mass for mainstream quark models. Indeed, a c¯
The now established [3] J P C = 1++ quantum numbers even more importantly — a corresponding wave-function
seem to imply that X(3872) is either the still unconfirmed component in the inner region of the same order of mag[2] χ0c1 (2 3P1 c¯
c) meson, or an axial-vector charmonium- nitude as that of the D0 D?0 channel, thus ruling out a
like state of a different kind. For a recent review, see e.g. pure molecular scenario for X(3872). Similar interpretations of X(3872) were concluded in the unquenched model
Ref. [4].
However, in order to understand the true nature of calculations of Refs. [7] and [8].
X(3872), one can ignore neither the presence of relatively
Besides the mentioned hadronic decays, X(3872) has
nearby 1++ states in the theoretical charmonium specalso
been observed [2] to decay in electromagnetic (EM)
trum, nor their strong coupling to the S-wave threshold
0 ¯ ?0
processes,
namely to γJ/ψ and γψ(2S). Such decays are
D D . In this spirit, the properties of X(3872) were revery
sensitive
to details of the X(3872) wave function, escently studied in Refs. [5, 6], by modelling it as an un0
pecially
in
its
inner
region, and so may discriminate among
quenched χc2 state with additional meson-meson (MM)
components, most importantly D0 D?0 .1 In the former pa- different microscopic models. Thus, the coordinate-space
per [5], a momentum-space calculation of X(3872) was method for unquenched quarkonium states employed in
carried out, employing the Resonance-Spectrum Expan- Ref. [6] appears to be the indicated approach for such a
sion (RSE), with all relevant two-meson channels included. calculation. Now, it was shown in Refs. [9, 10] that, in a
This work showed that the hadronic decays of X(3872) can multichannel system with one almost unbound channel,
thus be described quite accurately, dispensing with ad hoc more strongly bound channels should not be neglected
beforehand for processes in which the wave function at
1
For notational simplicity, we henceforth omit the bars over short distances is important. This is of course all the more
true for the D± D?∓ channel in the X(3872) case, which is
the anticharm mesons.
Prepared for submission to JHEP
HRI-P-14-10-001
arXiv:1411.1525v1 [hep-ph] 6 Nov 2014
h → γγ in U (1)R− lepton number model with a
right-handed neutrino
Sabyasachi Chakraborty,a,1 AseshKrishna Datta,b Sourov Roya
a
Department of Theoretical Physics, Indian Association for the Cultivation of Science, 2A & 2B
Raja S.C.Mullick Road, Jadavpur, Kolkata 700 032, INDIA
b
Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019, INDIA
E-mail: [email protected], [email protected], [email protected]
Abstract: We perform a detailed study of the signal rate of the lightest Higgs boson in the
diphoton channel (µγγ ), recently analyzed by both the ATLAS and CMS collaborations at
the Large Hadron Collider, in the framework of U (1)R − lepton number model with a right
handed neutrino superfield. The corresponding neutrino Yukawa coupling, ‘f ’, plays a very
important role in the phenomenology of this model. A large value of f ∼ O(1) provides an
additional tree level contribution to the lightest Higgs boson mass along with a very light
(mass ∼ a few hundred MeV) bino like neutralino and a small tree level mass of one of the
active neutrinos that is compatible with various experimental results. In the presence of
this light neutralino, the total decay width of the Higgs boson and its various branching
fractions are affected. When studied in conjunction with the recent LHC results, these put
significant constraints on the parameter space. The signal rate µγγ obtained in this scenario
is compatible with the recent results from both the ATLAS and the CMS collaborations
at 1σ level. A small value of ‘f ’, on the other hand, is compatible with a sterile neutrino
acting as a 7 keV dark matter that can explain the observation of a mono-energetic X-ray
photon line by the XMM-Newton X-ray observatory. Because of the absence of a light
neutralino, the total decay width of the lightest Higgs boson in this case remains close to
the SM expectation. Hence, in the small ‘f ’ scenario we obtain a relatively larger value of
µγγ which is closer to the central values reported recently by these two collaborations.
Keywords: Supersymmetry Phenomenology
1
Corresponding author.
Testing GeV-Scale Dark Matter with Fixed-Target Missing Momentum Experiments
Eder Izaguirre, Gordan Krnjaic, Philip Schuster, and Natalia Toro
Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada
(Dated: November 7, 2014)
We describe an approach to detect dark matter and other invisible particles with mass below
a GeV, exploiting missing energy-momentum measurements and other kinematic features of fixedtarget production. In the case of an invisibly decaying MeV–GeV-scale dark photon, this approach
can improve on present constraints by 2–6 orders of magnitude over the entire mass range, reaching
sensitivity as low as 2 ∼ 10−14 . Moreover, the approach can explore essentially all of the viable
parameter space for thermal or asymmetric dark matter annihilating through the vector portal.
arXiv:1411.1404v1 [hep-ph] 5 Nov 2014
I.
INTRODUCTION
Existing techniques to search for dark matter (DM)
are most effective in two regimes: if dark matter is heavy
like a WIMP [1–7], or if it is very light and coherent like
an axion field [8–13]. If dark matter is lighter than a few
GeV and not coherent, then direct detection techniques
are notoriously difficult. But some of the most appealing
dark matter scenarios overlap with this difficult category,
such as the case when dark matter and baryons have a
common origin with comparable number densities [14, 15]
or DM is part of a hidden sector (see [16] for a review).
This largely open field of GeV-scale dark matter possibilities offers well-motivated discovery opportunities and
is ripe for experimental exploration.
In either of the above scenarios, DM must interact with
the Standard Model (SM) to avoid overproduction in the
early universe. Among the simplest such interactions are
those mediated by a kinetically mixed gauge boson (A0 )
associated with a dark sector gauge symmetry [25, 26].
Light DM that primarily annihilates through an off-shell
A0 into Standard Model particles is largely unconstrained
by available data [16]. With light DM and mediator mass
scales m comparable, an acceptably small relic density
robustly bounds the dark sector coupling αD and kinetic
mixing (see Sec. 2) by
−10
2
(αD 2 )relic density >
∼ O(1) × 10 (100 MeV/m) (1)
This is an important benchmark level of sensitivity to
reach to decisively probe this broad and widely considered framework for light DM.
Recently, new beam-dump experiments have aimed to
produce light DM candidates and then observe their scattering in downstream detectors [20, 27–35]. This is a
compelling technique to discover light DM, but its reliance on a small re-scattering probability prevents this
approach from reaching the milestone sensitivity of Eq. 1.
Achieving this sensitivity requires the identification of
DM production events based solely on their kinematics,
which in fixed-target electron-nuclear collisions is quite
distinctive [36]. Light DM candidates produced in such
collisions carry most of the incident beam-energy, so a
forward detector that can efficiently capture the energy of
electron/hadron showers can be used to observe this signature above irreducible backgrounds (which are small)
and reducible backgrounds (which require aggressive rejection). In fact, an effort to exploit this feature and
search for light DM using a secondary beam of electrons
from SPS spills at CERN was proposed in [17].
Our goals in this paper are twofold. We first evaluate the ultimate limitations for fixed-target DM searches
using missing energy-momentum. While neutrino production reactions set an in-principle background floor,
in practice such an experiment will likely be limited by
instrumental backgrounds — specifically, detection inefficiencies that allow rare photo-production reactions to
mimic the missing energy-momentum signature. This
conclusion motivates experimental scenarios that can
more efficiently reject such backgrounds. We therefore propose an experimental setup optimized to measure the recoil electron’s kinematics and demonstrate
that this measurement allows significantly improved kinematic background rejection and in situ measurements of
detector inefficiencies. This approach can reach the milestone sensitivity (1) to robustly test vector portal light
DM over the entire mass range from MeV−GeV. Moreover, a new-physics interpretation of any positive signal
would be greatly bolstered by these additional kinematic
handles.
Figure 1 summarizes the potential sensitivity for a few
benchmark scenarios, including for the first time in the
literature a realistic calculation of the DM signal yields.
Belle-II could explore the remaining m >GeV portion of
this target if mono-photon triggers are implemented [18].
Beyond dark matter physics, the approach we advocate
will play an important role in improving sensitivity to kinetically mixed dark photons that decay invisibly, nicely
complementing the ongoing program of searches for visible decays [29, 30, 37–55]. Indeed, while the window
identified six years ago for visibly decaying dark photons
to explain the muon g − 2 anomaly has recently been
closed [56], the corresponding parameter space for invisibly decaying dark-photons has not been fully explored.
The approach outlined in this paper will cover the entire g − 2 anomaly region for invisible decays (as does the
proposal of [17]) and has sensitivity that extends beyond
any existing or planned experiment by several orders of
magnitude, in a manner largely insensitive to model details.
Section II summarize our benchmark model for light
dark matter interacting with the standard model through
November 6, 2014
arXiv:1411.1644v1 [hep-ex] 6 Nov 2014
Measurements of single top-quark production in pp collisions
by the CMS experiment
Andrey Popov on behalf of the CMS collaboration
Universit´e catholique de Louvain, Louvain-la-Neuve, Belgium
Also at Lomonosov Moscow state university, Moscow, Russia
A summary of studies of electroweak top-quark production performed
by the CMS collaboration is presented. The results include measurements
of production cross sections, extraction of the value of |Vtb |, determination
of W -boson helicity in top-quark decays and top-quark spin asymmetry,
and a search for anomalous couplings in the W tb vertex. No deviations
from predictions of the standard model are found.
PRESENTED AT
The 8th international workshop on the CKM unitarity
triangle (CKM 2014)
Vienna, Austria, September 8–12, 2014
1
Introduction
Top quark is the most massive known elementary particle and as such is often speculated to have a special sensitivity to possible physics beyond the standard model
(SM). At LHC it is produced predominantly in pairs via the strong interaction, but
electroweak production of single top quarks is not negligible. At leading order it
can be classified into three production channels, depending on the virtuality of the
involved W boson, as shown in Fig. 1.
q
q0
W
(a)
g
W
q¯0
t
b
(b)
¯b
W
b
t
t
b
g
W
b
t
q
t
(c)
Figure 1: Representative Feynman diagrams for electroweak top-quark production:
t-channel (a), tW -channel (b), and s-channel (c).
This paper summarises experimental studies of single top-quark production performed with the CMS detector [1]. It does not cover however flavour-changing neutral
currents discussed in [2] or searches of new particles in final states involving single
top quarks.
2
Cross sections and |Vtb|
Measurements in all three production channels were performed. Although applied
event selections depend on the target channel, the presence of a b-tagged jet, which is
a jet that is identified as stemming from hadronisation of a b quark, is required and
only semileptonic decays of the top quark with muons or electrons in the final state
are considered.
2.1
Measurement in the t channel
At LHC production in the t channel is the dominant of the three modes, and as
such was studied first. A prominent feature of this process is the presence of a lightflavour recoil jet (denoted q 0 in Fig. 1a) that is often forward. Thus, the experimental
signature of signal events is exactly one isolated muon or electron, a moderate missing
ET due to a neutrino, and two jets, only one of which is b-tagged. Main backgrounds
are top pair and W boson production.
The production
cross section was measured at centre-of-mass energies of 7 and
√
8 TeV. At s = 7 TeV three independent analyses were performed [3]. The first
1
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
arXiv:1411.1634v1 [hep-ex] 6 Nov 2014
CERN-PH-EP-2014-268
LHCb-PAPER-2014-058
November 7, 2014
Measurement of the CP -violating
phase β in B 0 → J/ψπ +π − decays
and limits on penguin effects
The LHCb collaboration†
Abstract
(
)
Time-dependent CP violation is measured in the B 0 → J/ψ π + π − channel for
each π + π − resonant final state using data collected with an integrated luminosity of
3.0 fb−1 in pp collisions using the LHCb detector. The final state with the largest rate,
◦
J/ψ ρ0 (770), is used to measure the CP -violating angle 2β eff to be (41.7 ± 9.6+2.8
−6.3 ) .
This result can be used to limit the size of penguin amplitude contributions to CP
(
)
violation measurements in, for example, B s0 → J/ψ φ decays. Assuming approximate
SU(3) flavour symmetry and neglecting higher order diagrams, the shift in the CP violating phase φs is limited to be within the interval [−1.05◦ , +1.18◦ ] at 95%
confidence level. Changes to the limit due to SU(3) symmetry breaking effects are
also discussed.
Submitted to Phys. Lett. B
c CERN on behalf of the LHCb collaboration, license CC-BY-4.0.
†
Authors are listed at the end of this letter.
EPJ Web of Conferences will be set by the publisher
DOI: will be set by the publisher
c Owned by the authors, published by EDP Sciences, 2014
New results on transverse spin asymmetries from COMPASS
Bakur Parsamyan1,2 , a
1
arXiv:1411.1568v1 [hep-ex] 6 Nov 2014
2
Dipartimento di Fisica Generale, Università di Torino, Torino, Italy
INFN, Sezione di Torino, Via P. Giuria 1, I-10125 Torino, Italy
Abstract. One of the important objectives of the COMPASS experiment is the exploration of transverse
spin structure of nucleon via spin (in)dependent azimuthal asymmetries in semi-inclusive deep inelastic
scattering (SIDIS) of polarized leptons (and soon also Drell-Yan (DY) reactions with π− ) off transversely polarized target. For this purpose a series of measurements were made in COMPASS, using
160 GeV/c longitudinally polarized muon beam and polarized 6 LiD and NH3 targets and are foreseen
with 190 GeV/c π− beam on polarized NH3 . The experimental results obtained by COMPASS for azimuthal effects in SIDIS play an important role in the general understanding of the three-dimensional
nature of the nucleon and are widely used in theoretical analyses and global data fits. Future first ever
polarized DY-data from COMPASS compared with SIDIS results will open a new chapter probing general principles of QCD TMD-formalism. In this review main focus will be given to the very recent
COMPASS results obtained for SIDIS transverse spin asymmetries from four "Drell-Yan" Q2 -ranges.
1 Introduction
Using standard notations SIDIS cross-section can be
written in a following model-independent way [1], [2]:
"
!#
dσ
α
y2
γ2
=
1
+
FUU
xyQ2 2 (1 − ε)
2x
dxdydzdP2hT dϕh dψ
n
p
φh
cos 2φh
× 1 + 2ε (1 + ε)Acos
cos 2φh
UU cos φh + εAUU
hp
i
φh
+ λ 2ε (1 − ε)Asin
LU sin φh
i
hp
φh
sin 2φh
2ε (1 + ε)Asin
sin 2φh
+ SL
UL sin φh + εAUL
h√
i
p
φh
+ S L λ 1 − ε2 ALL + 2ε (1 − ε)Acos
cos φh
LL
sin(φ −φ )
+ ST AUT h S sin (φh − φS )
sin(φ +φ )
+ εAUT h S sin (φh + φS )
sin(3φ −φ )
+ εAUT h S sin (3φh − φS )
p
φS
+ 2ε (1 + ε)Asin
sin φS
UT
p
sin(2φh −φS )
+ 2ε (1 + ε)AUT
sin (2φh − φS )
q
cos(φ −φ )
+ ST λ
1 − ε2 ALT h S cos (φh − φS )
p
φS
+ 2ε (1 − ε)Acos
cos φS
LT
p
cos(2φh −φS )
+ 2ε (1 − ε)ALT
cos (2φh − φS )
a e-mail: [email protected]
(1)
where, FUU = FUU,T + εFUU,L and ψ is the laboratory azimuthal angle of the scattered lepton (in DIS
kinematics dψ ≈ dφS ). Target transverse polarization dependent part of this general expression contains eight azimuthal modulations in the φh and φS azimuthal angles of the produced hadron and of the nucleon spin, correspondingly, see Fig. 1. Each modulation leads to a AwBTi (φh ,φs ) Target-Spin-dependent Asymmetry (TSA) defined as a ratio of the associated structure function to the unpolarized ones. Here the superscript of the asymmetry indicates corresponding modulation, the first and the second subscripts - respective
("U"-unpolarized,"L"-longitudinal and "T"-transverse)
polarization of beam and target. Five amplitudes which
depend only on S T are the Single-Spin Asymmetries
(SSA), the other three which depend both on S T and λ
(beam longitudinal polarization) are known as DoubleSpin Asymmetries (DSA). Amplitude of each modulation is scaled by a ε-dependent so-called depolarization
factor where:
ε=
1−y− 14 γ2 y2
,
1−y+ 12 y2 + 14 γ2 y2
γ=
2Mx
Q
(2)
Using similar notations, the general form of the singlepolarized (πN ↑ ) Drell-Yan cross-section (leading order
part) in terms of angular variables defined in CollinsSoper frame (Fig. 1) can be written in the following
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)
arXiv:1411.1559v1 [hep-ex] 6 Nov 2014
CERN-PH-EP-2014-245
Submitted to: Phys. Rev. D
Search for new phenomena in events with a
√photon and missing
transverse momentum in pp collisions at s = 8 TeV with the
ATLAS detector
The ATLAS Collaboration
Abstract
Results of a search for new phenomena in events with an energetic photon and large missing
transverse momentum with the ATLAS experiment at the LHC are reported. Data were collected
in proton–proton collisions at a center-of-mass energy of 8 TeV and correspond to an integrated
luminosity of 20.3 fb−1 . The observed data are well described by the expected Standard Model
backgrounds. The expected (observed) upper limit on the fiducial cross section for the production of
such events is 6.1 (5.3) fb at 95% confidence level. Exclusion limits are presented on models of new
phenomena with large extra spatial dimensions, supersymmetric quarks, and direct pair production of
dark-matter candidates.
c 2014 CERN for the benefit of the ATLAS Collaboration.
Reproduction of this article or parts of it is allowed as specified in the CC-BY-3.0 license.
Status and Implications of BSM Searches at the LHC
Eva Halkiadakis1 , George Redlinger2 , and David Shih3
arXiv:1411.1427v1 [hep-ex] 5 Nov 2014
1
Dept of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854
2
3
Physics Dept, Brookhaven National Laboratory, Upton, NY 11973
NHETC, Dept of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854
Abstract
The LHC has collided protons on protons at center-of-mass energies of 7 and 8 TeV
between 2010-2012, referred to as the Run I period. We review the current status of
searches for new physics beyond the Standard Model at the end of Run I by the ATLAS
and CMS experiments, limited to the 8 TeV search results published or submitted for
publication as of the end of February 2014. We discuss some of the implications of
these searches on the existence of TeV scale new physics, with a special focus on two
open questions: the hierarchy problem, and the nature of dark matter. Finally, we give
an outlook for the future.
UMN-TH-3407/14
A Soft-Wall Dilaton
Peter Coxa,† and Tony Gherghettab,‡
a ARC
arXiv:1411.1732v1 [hep-th] 6 Nov 2014
Centre of Excellence for Particle Physics at the Terascale,
School of Physics, University of Melbourne, Victoria 3010, Australia
b School of Physics & Astronomy, University of Minnesota,
Minneapolis, MN 55455, USA
Abstract
We study the properties of the dilaton in a soft-wall background using two solutions
of the Einstein equations. These solutions contain an asymptotically AdS metric with
a nontrivial scalar profile that causes both the spontaneous breaking of conformal invariance and the generation of a mass gap in the particle spectrum. We first present
an analytic solution, using the superpotential method, that describes a CFT spontaneously broken by a finite dimensional operator in which a light dilaton mode appears
in the spectrum. This represents a tuning in the vanishing of the quartic coupling in
the effective potential that could be naturally realised from an underlying supersymmetry. Instead, by considering a generalised analytic scalar bulk potential that quickly
transitions at the condensate scale from a walking coupling in the UV to an order-one
β-function in the IR, we obtain a naturally light dilaton. This provides a simple example for obtaining a naturally light dilaton from nearly-marginal CFT deformations in
the more realistic case of a soft-wall background.
†
‡
Email: [email protected]
Email: [email protected]
Prepared for submission to JHEP
arXiv:1411.1669v1 [hep-th] 6 Nov 2014
On the Subleading-Soft Behaviour of QCD Amplitudes
Hui Luo,a,b,c Pierpaolo Mastrolia,a,b,d and William J. Torres Bobadillaa,b
a
Dipartimento di Fisica ed Astronomia, Universit`
a di Padova, Via Marzolo 8, 35131 Padova, Italy
b
INFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy
c
SISSA, Via Bonomea 265, 34136 Trieste, Italy
d
Max-Planck-Institut f¨
ur Physik, F¨
ohringer Ring 6, 80805 M¨
unchen, Germany
Abstract: We elaborate on the radiative behaviour of tree-level scattering amplitudes in the soft regime.
We show that the sub-leading soft term in single-gluon emission of quark-gluon amplitudes in QCD is
controlled by differential operators, whose universal form can be derived from both on-shell recursion
relation and gauge invariance, as it was shown to hold for graviton- and gluon-scattering.
Keywords: QCD, scattering amplitudes
Approaching Conformality
arXiv:1411.1657v1 [hep-lat] 6 Nov 2014
Maria Paola Lombardo
INFN-Laboratori Nazionali di Frascati
E-mail: [email protected]
Kohtaroh Miura
Kobayashi-Maskawa Institute for the Origin of Particles and the Universe(KMI), Nagoya
University
E-mail: [email protected]
Tiago Nunes da Silva∗
Van Swinderen Institute, University of Groningen
E-mail: [email protected]
Elisabetta Pallante
Van Swinderen Institute, University of Groningen
E-mail: [email protected]
We investigate the preconformal region of the phase diagram of SU(3) theories with fundamental flavors. We have simulated SU(3) theories with six and eight fundamental flavors at volumes
323 ×64. We use the generated configurations to measure the string tension σ and the w0 scale set√
ting quantity extracted from the gradient flow. We show preliminary results on the ratios Tc / σ
and Tc w0 . We compare them to the behavior obtained at smaller N f and discuss the implications
of our results.
The 32nd International Symposium on Lattice Field Theory,
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/
November 7, 2014
1:21
WSPC/INSTRUCTION FILE
CKWFin
arXiv:1411.1655v1 [astro-ph.HE] 6 Nov 2014
Modern Physics Letters A
© World Scientific Publishing Company
EFFECTS OF DARK ATOM EXCITATIONS
JEAN-RENE CUDELL
IFPA, D´
ep. AGO, Universit´
e de Li`
ege, Sart Tilman, 4000 Li`
ege, Belgium
[email protected]
MAXIM YU. KHLOPOV
National Research Nuclear University ”MEPHI” (Moscow Engineering Physics Institute) and
Centre for Cosmoparticle Physics ”Cosmion” 115409 Moscow, Russia
APC laboratory 10, rue Alice Domon et L´
eonie Duquet
75205 Paris Cedex 13, France
[email protected]
QUENTIN WALLEMACQ
IFPA, D´
ep. AGO, Universit´
e de Li`
ege, Sart Tilman, 4000 Li`
ege, Belgium
[email protected]
Received (Day Month Year)
Revised (Day Month Year)
New stable quarks and charged leptons may exist and be hidden from detection, as they
are bound by Coulomb interaction in neutral dark atoms of composite dark matter. This
possibility leads to fundamentally new types of indirect effects related to the excitation
of such dark atoms followed by their electromagnetic de-excitation. Stable -2 charged
particles O−− , bound to primordial helium in O-helium (OHe) atoms, represent the
simplest model of dark atoms. Here we consider the structure of OHe atomic levels
which is a necessary input for the indirect tests of such composite dark matter scenarios,
and we give the spectrum of electromagnetic transitions from the levels excited in OHe
collisions.
Keywords: Elementary particles; composite dark matter; dark atoms; energy levels; cosmic electromagnetic radiation; indirect effects of dark matter.
PACS Nos.: 95.35.+d, 97.80.Jp, 95.85.Pw
1. Introduction
According to modern cosmology, dark matter corresponds to ∼ 25% of the total cosmological density, is nonbaryonic and consists of new stable particles. Such particles
(see e.g. references 1 and 2 for a review) should be stable, saturate the measured
dark matter density and decouple from plasma and radiation at least before the beginning of the matter-dominated era. The easiest way to satisfy these conditions is
to involve neutral elementary weakly interacting massive particles (WIMPs). However it is not the only particle physics solution for the dark matter problem and
1
Importance of different energy loss effects in jet suppression at RHIC
Bojana Blagojevic1 and Magdalena Djordjevic1
arXiv:1411.1649v1 [nucl-th] 6 Nov 2014
1
Institute of Physics Belgrade, University of Belgrade, Serbia
(Dated: November 7, 2014)
Jet suppression is considered to be an excellent probe of QCD matter created in ultra-relativistic
heavy ion collisions. Our theoretical predictions of jet suppression, which are based on our recently
developed dynamical energy loss formalism, show a robust agreement with various experimental
data, which spans across different probes, experiments (RHIC and LHC) and experimental conditions (i.e. all available centrality regions). This formalism includes several key ingredients, such
as inclusion of dynamical scattering centers, finite size QCD medium, collisional energy loss, finite
magnetic mass and running coupling. While these effects have to be included based on theoretical
grounds, it is currently unclear what is their individual importance in accurately explaining the
experimental data, in particular because other approaches to suppression predictions commonly neglect some - or all - of these effects. To address this question, we here study relative importance of
those effects in obtaining accurate suppression predictions for D mesons (a clear energy loss probe)
in RHIC experiments. We obtain that several different ingredients are responsible for the accurate
predictions, i.e. the robust agreement with the data is a cumulative effect of all ingredients rather
than a consequence of one dominant effect.
PACS numbers: 12.38.Mh; 24.85.+p; 25.75.-q
INTRODUCTION
Suppression of high transverse momentum light and
heavy flavor observables [1] is considered to be an excellent probe of QCD matter created in ultra-relativistic
heavy ion collisions at RHIC and LHC. One of the major
goals of these experiments is mapping the QGP properties, which requires comparing available suppression data
with the theoretical predictions [2–4]; such comparison
tests different theoretical models and provides an insight
into the underlying QGP physics. It is generally considered that the crucial ingredient for reliable suppression
predictions is accurate energy loss calculation.
We consequently developed the dynamical energy loss
formalism which includes the following effects: i) dynamical scattering centers, ii) QCD medium of a finite size
[5, 6], iii) both radiative [5, 6] and collisional [7] energy losses, iv) finite magnetic mass effects [8] and v)
running coupling [9]. This energy loss formalism has
been incorporated into a numerical procedure [9] that allows generating state-of-the art suppression predictions.
These predictions are able to explain heavy flavor puzzles
at both RHIC [10] and LHC [11] and, in general, show a
very good agreement with the available suppression data
at these experiments, for a diverse set of probes [9, 10]
and centrality regions [12].
Such good agreement of the theoretical predictions
with the experimental data however raises a question of
which energy loss effects are responsible for accurately
explaining the data. In other words, is there a single
energy loss effect which is responsible for the good agreement, or this agreement is a cumulative effect of several
smaller improvements. This issue is moreover important,
given the fact that various approaches to energy loss cal-
culations neglect some (or most) of these effects.
Consequently, we here address the importance of different energy loss ingredients in suppression calculations.
For this purpose, it would be optimal to have a probe that
is sensitive only to energy loss, i.e. for which fragmentation and decay functions do not play a role. D meson
suppression is such a probe, since fragmentation functions do not modify bare charm quark suppression, as
previously shown in [10, 11]; To explore different energy
loss approximations, which are used in RHIC suppression predictions, we here concentrate on D meson suppression in central 200 GeV Au+Au collisions at RHIC.
Our approach is to systematically include different energy loss effects. In particular, we first compare relative
importance of radiative and collisional contribution to D
meson suppression predictions, to assess the adequacy of
historically widely used static approximation. We then
investigate the importance of including the dynamical
scattering centers, followed by collisional energy loss and
finite size (LPM) effects. Finally, we also address the
importance of including Ter-Mikayelian effect [13], finite
magnetic mass and the running coupling.
THEORETICAL AND COMPUTATIONAL
FRAMEWORKS
We first provide a brief overview of the computational
framework and the dynamical energy loss formalism; as
mentioned above this formalism leads to a very good
agreement with the suppression data. We will also introduce how the energy loss expression is modified, as
different ingredients are excluded from the full energy
loss formalism. Note that, in the Results and Discussion
section, we will for clarity address different energy loss
Calculation of BSM Kaon B-parameters using
Staggered Quarks
arXiv:1411.1501v1 [hep-lat] 6 Nov 2014
Yong-Chull Jang, Hwancheol Jeong, Jangho Kim, Seonghee Kim, Weonjong Lee,
Jaehoon Leem∗, Jeonghwan Pak, Sungwoo Park
Lattice Gauge Theory Research Center, CTP, and FPRD,
Department of Physics and Astronomy, Seoul National University, Seoul, 151-747, South Korea
E-mail: [email protected]
Chulwoo Jung, Hyung-Jin Kim
Physics Department, Brookhaven National Laboratory, Upton, NY11973, USA
E-mail: [email protected]
Stephen R. Sharpe
Physics Department, University of Washington, Seattle, WA 98195-1560, USA
E-mail: [email protected]
Boram Yoon
Los Alamos National Laboratory,
Theoretical Division T-2, MS B283,
Los Alamos, NM 87545, USA
E-mail: [email protected]
SWME Collaboration
We present updated results for kaon B-parameters for operators arising in models of new physics.
We use HYP-smeared staggered quarks on the N f = 2 + 1 MILC asqtad lattices. During the last
year we have added new ensembles, which has necessitated chiral-continuum fitting with more
elaborate fitting functions. We have also corrected an error in a two-loop anomalous dimension
used to evolve results between different scales. Our results for the beyond-the-Standard-Model Bparameters have total errors of 5 − 10%. We find that the discrepancy observed last year between
our results and those of the RBC/UKQCD and ETM collaborations for some of the B-parameters
has been reduced from 4−5 σ to 2−3 σ .
32nd International Symposium on Lattice Field Theory - LATTICE 2014
June 23 - June 28, 2014
Columbia University
∗ Speaker.
c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
The nucleon resonances in the J/ψ → p¯
pη ′ decay
Xu Cao1,2,3∗ and Ju-Jun Xie1,2†
arXiv:1411.1493v1 [nucl-th] 6 Nov 2014
1
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
2
State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,
Chinese Academy of Sciences, Beijing 100190, China
3
Kavli Institute for Theoretical Physics China (KITPC),
Chinese Academy of Sciences, Beijing 100190, China
We are aiming to study the J/ψ → p¯
pη ′ decay in an isobar model and the effective Lagrangian
approach. After a careful exploration of the contributions of the S11 (1535), P11 (1710), P13 (1900),
S11 (2090) and P11 (2100) resonances, we conclude that either a subthreshold resonance or a broad
P -wave state in the near threshold range seems to be indispensable to describe present data of the
πN → η ′ N . Furthermore, at least one broad resonance above η ′ N threshold is preferred. With this
detailed analysis, we could give the invariant mass spectrum and Dalitz plot of the J/ψ → p¯
pη ′
decay for the purpose of assisting the future detailed partial wave analysis. It is found that the
J/ψ → p¯
pη ′ data are useful for disentangling the above or below threshold resonant contribution,
though it still further needs the differential cross section data of πN → η ′ N to realize some of the
resonant and the non-resonant contribution. Our results are enlightening for the η ′ N production
mechanism and the properties of the nucleon resonances with the mass around 2.0 GeV.
PACS numbers: 13.20.Gd, 13.75.Gx, 14.20.Gk
I.
INTRODUCTION
In recent years, plenty of information on nucleon resonances [1] has been obtained by a wealth of phenomenological studies on numerous data of the πN , γN , eN
reactions [2–22] and pN collisions [23–35]. However, despite a great deal of theoretical and experimental efforts,
our knowledge of nucleon resonances around 2.0 GeV is
still scarce because of the presence of many resonances
and opening channels in this energy region. Alternatively, the hadronic decay channels of heavy quarkonium
have attracted much attention due to their advantage
in extracting empirical information of resonances with
isospin 1/2. In this area, a lot of progress have been
made on the study of the decay of the charmonium
states, e.g. J/ψ, ψ(3686), ψ(3770) and χcJ states by
BES and CLEO collaborations [36–46]. In particular,
it is advanced by the wide implementation of the tools
of partial wave analysis (PWA) [47–49] to the tremendous (up to billion) events accumulated with the BESIII
detector at the BEPCII facility. In these fruitful PWA
¯ π channels,
works which mainly concentrate on the N N
∗
not only the peak of known N resonances are directly
observed, but also the evidence of several new resonances
with higher mass are found [36–38], e.g. N ∗ (2040) with
J P = 3/2+ found in J/ψ → p¯
pπ 0 [36] and N ∗ (2300) with
P
+
∗
J = 1/2 and N (2570) with J P = 5/2− appeared in
ψ(3686) → p¯
pπ 0 [38].
It is indispensable to explore the decay modes with
final mesons other than π-meson in order to search for
the missing states coupling weakly to π-meson. Unfortu-
∗ Electronic
† Electronic
address: [email protected]
address: [email protected]
nately, up to date we know little about the coupling of
the η ′ -, ω-, and φ-mesons to nucleon resonances [50] and
the interaction of these mesons with the nucleon [51]. In
past decades, the production of these mesons in the γN
and pN reactions have been widely investigated, mainly
motivated by the increasing data measured by CLAS,
CBELSA and COSY groups [24–31, 52–54]. But the results are quite inconclusive for the moment. It is still
not firmly established which resonance(s) play the important role in these reactions, and it is still controversial whether the sub-threshold resonances have essential
contributions. In order to resolve these ambiguities, it is
natural to deliver our sight into the strangeness decay of
¯ η′ , N N
¯ φ, and the associate
charmonium states, e.g. N N
¯ and N ΣK
¯ [42].
strangeness decay channels N ΛK
¯ η ′ deThe invariant mass spectrums of the J/ψ → N N
cay cover the energy range from mN +mη′ ≃ 1.90 GeV to
mJ/ψ − mN ≃ 2.16 GeV, where the debatable P13 (1900)
state [4, 7] and the long-sought third S11 and P11 states
at about 2100 MeV [2–7] are expected to be present. The
P13 (1900) state, which is unfavored by diquark models,
is considered at the early stage of Giessen model [7–11]
and KSU survey [14, 15]. The Bonn-Gatchina partial
wave analysis find its evidence in the KΣ photoproduction data only recently [3, 4], but the latest GWU analysis do not include it as before [16]. The existence of
the third S11 and P11 states could shed light on the spin
quartet of nucleon resonances, which is disputed in classical diquark models [5]. This topic is interesting also
because it could shed light on the nature and the internal
structure of relevant nucleon resonances which may have
large s¯
s component [50]. It can also serve as a guideline
to the future detailed PWA in view of the current scarce
information on these resonances.
In the mentioning decay channels, the possible background contribution - the nucleon pole - has been calcu-
Constraining Inflationary Dark Matter in the Luminogenesis
Model
Pham Q. Hung1, 2, ∗ and Kevin J. Ludwick1, †
1
Department of Physics, University of Virginia, Charlottesville, VA 22904-4714, USA
2
Center for Theoretical and Computational Physics,
Hue University College of Education, Hue, Vietnam
arXiv:1411.1731v1 [hep-ph] 6 Nov 2014
Abstract
Using renormalization-group flow and cosmological constraints on inflation models, we exploit a
unique connection between cosmological inflation and the dynamical mass of dark-matter particles
in the luminogenesis model, a unification model with the gauge group SU (3)C × SU (6) × U (1)Y ,
which breaks to the Standard Model with an extra gauge group for dark matter when the inflaton
rolls into the true vacuum. In this model, Inflaton decay gives rise to dark matter, which in turn
decays to luminous matter in the right proportion that agrees with cosmological data. Some attractive features of this model include self-interacting dark matter, which may resolve the problems
of dwarf-galaxy structures and dark-matter cusps at the centers of galaxies.
∗
†
[email protected]
[email protected]
1
Nucleon structure in a light-front quark model
consistent with quark counting rules and data
Thomas Gutsche,1 Valery E. Lyubovitskij,1, 2, 3 Ivan Schmidt,4 and Alfredo Vega5, 6
arXiv:1411.1710v1 [hep-ph] 6 Nov 2014
1
Institut f¨
ur Theoretische Physik, Universit¨
at T¨
ubingen,
Kepler Center for Astro and Particle Physics, Auf der Morgenstelle 14, D-72076 T¨
ubingen, Germany
2
Department of Physics, Tomsk State University, 634050 Tomsk, Russia
3
Mathematical Physics Department, Tomsk Polytechnic University, Lenin Avenue 30, 634050 Tomsk, Russia
4
Departamento de F´ısica y Centro Cient´ıfico Tecnol´
ogico de Valpara´ıso (CCTVal),
Universidad T´ecnica Federico Santa Mar´ıa, Casilla 110-V, Valpara´ıso, Chile
5
Instituto de F´ısica y Astronom´ıa, Universidad de Valpara´ıso, Avenida Gran Breta˜
na 1111, Valpara´ıso, Chile
6
Centro de Astrof´ısica de Valpara´ıso, Avenida Gran Breta˜
na 1111, Valpara´ıso, Chile
(Dated: November 7, 2014)
Using global fits of valence u and d quark parton distributions and data on quark and nucleon
form factors in the Euclidean region, we derive a light-front quark model for the nucleon structure
consistent with quark counting rules.
PACS numbers: 12.38.Lg, 13.40.Gp, 14.20.Dh, 14.65.Bt
Keywords: nucleons, light-front quark model, quark counting rules, parton distributions, form factors
I.
INTRODUCTION
The main objective of this paper is to continue our
study of a phenomenological light-front wave function
(LFWF) for the nucleon started as in Ref. [1]. We derived a LFWF for hadrons both for pions and nucleons which at an initial scale is constrained by the softwall AdS/QCD model, and which at higher scales gives
the correct scaling behavior of parton distributions and
form factors. The explicit form of the wave function at
large scales is extracted from the hard evolution of parton distribution functions (PDFs) and generalized parton distributions (GPDs). The proposed wave function
produces form factors consistent with quark counting
rules [2] and also gives predictions for the corresponding parton distributions. In our considerations we obtained harder PDFs in comparison with the results of
global fits (see e.g. results of Martin, Stirling, Thorne
and Watt (MSTW) [3]). The reason for a softening of the
PDFs was discussed in the pion case in Ref. [4]. There
it was clearly demonstrated that the inclusion of nextto-leading logarithmic (NLL) threshold resummation effects, due to collinear and soft gluon contributions, leads
to a softer pion PDF [4]. This result also shows that we
should take into account these resummation effects and
derive an improved nucleon LFWF. In Ref. [5] we demonstrate how to derive in the case of the pion a LFWF
producing a softer PDF as in Ref. [4] and a pionic electromagnetic form factor consistent with data and quark
counting rules. Here we extend this idea to the case of
the nucleon. We propose a LFWF for the nucleon modelled as a quark-scalar diquark bound state, with a specific dependence on the transverse momentum k⊥ and
the light-cone variable x. This LFWF produces PDFs
for valence u- and d-quark found in the global fits of
Ref. [3]. It also describes the electromagnetic form factors of the nucleon including their flavor decomposition
into u and d quark form factors up to values of the mo-
mentum transfer squared Q2 = 30 GeV2 in the Euclidean
region (for recent overview of experimental and theoretical progress in study of nucleon electromagnetic structure
see e.g. Refs. [6]-[8]). It is important to stress that the
calculated nucleon electromagnetic form factors are consistent with quark counting rules for large values of Q2 .
II.
LIGHT-FRONT QUARK-DIQUARK MODEL
FOR THE NUCLEON
In this section we propose a phenomenological LFWF
ψ(x, k⊥ ) for the nucleon, set up as a bound state of an
active quark and a spectator scalar diquark. This LFWF
is able to produce the u- and d-quark PDFs derived in the
global fits of Ref. [3] and generates electromagnetic form
factors of nucleons including their flavor decomposition
which are consistent with data.
First we collect the well-known decompositions [9] of
N
the nucleon Dirac and Pauli form factors F1,2
(N = p, n)
in terms of the valence quarks distributions in nucleons
q
with F1,2
(q = u, d), which then are related to the GPDs
q
(H and E q ) [10] of valence quarks
2 u(d) 2
1 d(u)
Fi (Q ) − Fi (Q2 ) ,
3
3
Z 1
F1q (Q2 ) =
dx Hq (x, Q2 ) ,
p(n)
Fi
(Q2 ) =
(1)
0
F2q (Q2 ) =
Z
0
1
dx E q (x, Q2 ) .
At Q2 = 0 the GPDs are related to the quark densities
— valence qv (x) and magnetic Eq (x) as
Hq (x, 0) = qv (x) ,
E q (x, 0) = E q (x) ,
(2)
Nuclear Physics B
Proceedings
Supplement
Nuclear Physics B Proceedings Supplement 00 (2014) 1–6
Inhomogeneous phases and chiral symmetry breaking
Stefano Carignano, Efrain J. Ferrer, and Vivian de la Incera
arXiv:1411.1686v1 [hep-ph] 6 Nov 2014
University of Texas at El Paso, Department of Physics, 500 W University Ave., El Paso, TX 79968
Abstract
A significant fraction of the current efforts in the QCD research community is focused on characterizing the phases
of strong-interaction matter that occur at finite densities and temperatures. So far, most of the experimental probes
have been limited to the relatively narrow window of the QCD phase diagram characterized by high temperatures and
low chemical potentials, explored in high-energy ion collision experiments at RHIC and LHC. More recently, some
new insight on the finite chemical potential region has been obtained by the energy-beam scan program at RHIC,
aimed at possibly determining the existence of a critical point in the QCD phase transition. On the theoretical side,
studies of strong interactions are also limited by the reliability of available methods. While the zero density, finite
temperature region or the zero temperature, superdense region can be investigated with the help of well-established
approaches like lattice and weakly coupled QCD respectively, the study of the intermediate densities and temperatures
region has to rely on effective models and nonperturbative methods, some of which are still being developed. In the
past few years, a growing number of compelling arguments, backed up by model calculations, pointed out that the
intermediate-density region of the QCD phase diagram may be characterized by the formation of inhomogeneous
condensates which spontaneously break some of the spatial symmetries of the theory. In the following we provide
a brief recapitulation of these arguments and describe some recent results in a 3+1-dimensional QCD-inspired NJL
model with quark-hole condensation in the form of a plane wave in the scalar and tensor channels. This model exhibits
particular features in close analogy to its 1+1-dimensional counterpart, most notably an asymmetric spectral density
and the arising of an anomalous contribution to the free energy.
Keywords: QCD phases, inhomogeneous condensates, quark-hole pairing
1. The Case for Inhomogeneous Phases
Mapping all the phases of QCD in the temperaturedensity plane is a goal intensely sought after by many
theoretical and experimental efforts [1]. Thanks to the
asymptotic freedom properties of the theory, the extreme regions of the QCD phase diagram are weakly
coupled and hence well understood; they are the quarkgluon plasma in the high-temperature/low-density corner and the Color-Flavor-Locked (CFL) superconducting phase [2] on the opposite side. At low temperatures
and densities quarks are confined inside hadrons, whose
interactions can be phenomenologically described by
conventional nuclear physics.
Somewhere in the region of intermediate tempera-
tures and densities, one expects two kinds of phase transitions to occur, the first related to deconfinement and
liberations of quark degrees of freedom from hadrons,
the second associated to the restoration of chiral symmetry, which is spontaneously broken in vacuum. Indeed, it is known that at low temperatures and densities,
quarks acquire a large constituent mass due to the formation of a (spatially homogeneous) chiral condensate
as a result of quarks-antiquark pairing. With increasing density, this condensate becomes disfavored due to
the high energy cost (at least twice the Fermi energy)
required to excite the antiquarks from the Dirac sea to
the Fermi surface. What phase forms when this “traditional” vacuum chiral condensate disappears is not
arXiv:1411.1665v1 [hep-ph] 6 Nov 2014
Dalitz plot studies in hadronic charm decays
Leonard Le´
sniak
Division of Theoretical Physics, The Henryk Niewodnicza´
nski Institute of Nuclear
Physics, Polish Academy of Sciences, 31-342 Krak´ow, POLAND
Recent studies of hadronic D-meson decays are reported. Some experimental searches of CP -symmetry violation using model independent
methods are presented. An importance of unitarity constraints in construction of phenomenological models of the D-meson decays is underlined. The theoretical model of the D 0 → KS0 π + π − decays, including
some two-body unitarity constraints, is described. Then a comparison
of the model results with the Belle collaboration data is made. The results on the CP -violation in the D 0 → KS0 π + π − decays are given and
the necessity to consider the CP -violation in the subsequent KS0 decays
is emphasized.
PRESENTED AT
the 8th International Workshop on the CKM Unitarity
Triangle (CKM 2014), Vienna, Austria, September 8-12,
2014
1
Introduction
Studies of the charm meson decays into multimeson final states have many aspects.
0
In particular, one can indicate measurements of the D 0 − D mixing parameters and
the Cabibbo-Kobayashi-Maskawa angle γ (or φ3 ), and searches of CP violation. Understanding the final state strong interactions between the produced particles, development of the model independent methods or a construction of the models satisfying
unitarity, analyticity and chiral symmetry constraints are other important topics.
Also improving the isobar models frequently used in analyses of experimental data is
highly desirable.
2
Search for CP violation in model independent
Dalitz plot analyses
Density distributions of events in the Dalitz plots are studied in three-body D-meson
decays. Recently, binned or unbinned methods in searches for CP violation effects
in the model independent Dalitz plot analyses are applied. Different variables are
used in these studies. For example, in the BABAR collaboration analysis of the
D ± → K + K − π ± decays [1] the so-called normalized residual variables ∆i are used
ni (D + ) − ni (D − )
,
∆i = q
σi2 (D + ) + R2 σi2 (D − )
(1)
where ni (D + ), ni (D − ) are numbers of signal events in the i-th bin of the Dalitz
plot, σi2 (D + ) and σi2 (D − ) are the statistical uncertainties. The correction factor,
P
P
R = ni (D + )/ ni (D − ), is used to remove the production or detection asymmetries. In the recent publication [2] devoted to the search of the CP violation in the
i
D ± → π + π − π ± decays the LHCb collaboration has used a similar variable SCP
, called
significance:
+
−
ni (D ) − ni (D )
i
SCP
=q
.
(2)
R[ni (D + ) + ni (D − )]
i
In absence of CP violation the distributions of the variables ∆i and SCP
are standard
normal Gaussian functions. In Ref. [2] the LHCb collaboration has also used the
unbinned k-nearest neighbour method. In this technique one chooses nk nearest
neighbour events in the combined D + and D − samples with N + and N − events.
Then the test variable T is defined as
T =
nk
N +X
+N − X
1
I(i, k),
nk (N + + N − ) i=1 k=1
1
(3)
Preprint typeset in JHEP style - HYPER VERSION
DAMTP-2014-79
arXiv:1411.1663v1 [hep-ph] 6 Nov 2014
MFV Reductions of MSSM Parameter Space
S.S. AbdusSalam,a,b∗ C.P. Burgessc,d,e† and F. Quevedob,f ‡
a
b
c
d
e
f
INFN, Sez. di Roma, P.le A. Moro 2, I-00185 Roma, Italia
The Abdus Salam ICTP, Trieste, Italy
Department of Physics & Astronomy, McMaster University, Hamilton ON, Canada
Perimeter Institute for Theoretical Physics, Waterloo, ON, Canada
Division PH -TH, CERN, CH-1211, Gen`eve 23, Suisse
DAMTP, Cambridge University, Cambridge, UK
Abstract: The 100+ free parameters of the minimal supersymmetric standard model
(MSSM) make it computationally difficult to compare systematically with data, motivating
the study of specific parameter reductions such as the cMSSM and pMSSM. Here we instead
study the reductions of parameter space implied by using minimal flavour violation (MFV)
to organise the R-parity conserving MSSM, with a view towards systematically building in
constraints on flavour-violating physics. Within this framework the space of parameters is
reduced by expanding soft supersymmetry-breaking terms in powers of the Cabibbo angle,
leading to a 24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and
MSSM-42 respectively), depending on the order kept in the expansion. We provide a
Bayesian global fit to data of the MSSM-30 parameter set to show that this is manageable
with current tools. We compare the MFV reductions to the 19-parameter pMSSM choice
and show that the pMSSM is not contained as a subset. The MSSM-30 analysis favours
a relatively lighter TeV-scale pseudoscalar Higgs boson and tan β ∼ 10 with multi-TeV
sparticles.
Keywords: Supersymmetry, Supersymmetric Standard Model, MSSM, Flavour
violation, LHC, Higgs mass, Bayesian.
∗
[email protected]
[email protected]
‡
[email protected]
†
BARI-TH/2014-693
November 7, 2014
arXiv:1411.1642v1 [hep-ph] 6 Nov 2014
New Physics Scenarios in b → c`ν ` decays
Fulvia De Fazio
Istituto Nazionale di Fisica Nucleare - Sezione di Bari
Via Orabona 4, I-70126 Bari, ITALY
B(B → D(∗) τ ν τ )
B(B → D(∗) µν µ )
deviate from the Standard Model predictions at the global level of 3.4σ. A
possibility to reproduce these experimental ratios without affecting other
modes which do not show similar deviations is to consider new physics
scenarios producing an additional tensor operator in the effective weak
Hamiltonian. I describe the impact of such an operator in semileptonic
B → D(∗) modes and in semileptonic B and Bs decays to excited positive parity charmed mesons. In particular, I discuss the most effective
observables able to discriminate new physics from the Standard Model.
The latest BaBar measurements of the ratios R(D(∗) ) =
PRESENTED AT
8th International Workshop on the CKM Unitarity Triangle
(CKM 2014),
Vienna, Austria, September 8-12, 2014
1
Introduction
Semileptonic decays induced by the b → c`ν ` transition are the cleanest modes to
measure the element Vcb of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. Recently, the possibility to use them to test lepton flavour universality and to reveal
new physics (NP) effects emerged, prompted by the BaBar Collaboration results [1]:
B(B − → D0 τ − ν τ )
= 0.429 ± 0.082 ± 0.052 ,
B(B − → D0 `− ν ` )
B(B − → D∗0 τ − ν τ )
−
∗
R (D ) =
= 0.322 ± 0.032 ± 0.022 ,
B(B − → D∗0 `− ν ` )
R− (D) =
0
R0 (D) =
B(B → D+ τ − ν τ )
0
B(B → D+ `− ν ` )
0
R0 (D∗ ) =
= 0.469 ± 0.084 ± 0.053 ,
∗+ −
B(B → D τ ν τ )
0
B(B → D∗+ `− ν ` )
= 0.355 ± 0.039 ± 0.021
(1)
(the first and second error are the statistic and systematic uncertainty, respectively).
As I discuss in the following, the results in (1) globally deviate at 3.4σ level with
respect to the Standard Model (SM) predictions [1, 2], and they might be due to
new particles with large couplings to the heavier fermions, namely charged scalars
contributing to tree-level b → c`ν transitions [2, 3]. However, if such new particles
exist, they should also affect the purely leptonic B − → τ − ν τ mode, for which the
most recent experimental branching ratio determinations are compatible with the
SM prediction [4]. To assess whether the results in (1) are a signal of NP, one should
investigate which NP scenario can reproduce them without affecting the leptonic
mode. Here, I summarize the analysis in [5] devoted to such an issue.
2
Exclusive b → c`ν ` decays
A modification of the SM effective weak Hamiltonian that produces a variation of the
ratios (1), leaving the purely leptonic B decays unaffected, is
h
i
GF
Hef f = √ Vcb cγµ (1 − γ5 )b `γ µ (1 − γ5 )ν ` + `T cσµν (1 − γ5 )b `σ µν (1 − γ5 )ν ` . (2)
2
GF is the Fermi constant, and a new tensor operator has been introduced, with the
τ
coupling `T assumed to mainly contribute for ` = τ : e,µ
T = 0 and T ≡ T . Physical
observables allow us to constrain this coupling.
To compute the branching ratios in (1), the hadronic matrix element of the Hamiltonian (2) between the B and D(∗) mesons are required. In the case of B → D`ν ` ,
1
arXiv:1411.1641v1 [hep-ph] 6 Nov 2014
Scalar coupling limits with unitarity, stability and
diphoton Higgs decay from LHC in an U (1)0 model plus
a scalar dark matter
R. Mart´ınez∗, J. Nisperuza†, F. Ochoa‡, J. P. Rubio§, C.F. Sierra¶
Departamento de F´ısica, Universidad Nacional de Colombia,
Ciudad Universitaria, Bogot´a D.C.
November 7, 2014
Abstract
In the context of an nonuniversal U (1)0 extension of the standard model free from
anomalies, we introduce a complex scalar singlet candidate to be dark matter. In
addition, an extra scalar doublet and a heavy scalar singlet are required to provide
masses to all fermions and to break spontaneously the symmetries. From unitarity and
stability of the Higgs potential, we find the full set of bounds and order relations for the
scalar coupling constants. Using recent data from the CERN-LHC collider, we study
the signal strenght of the diphoton Higgs decay Rγγ , which imposes very stringent
bounds to the scalar couplings and other scalar parameters. We obtain constraints in
different scenarios of the space of parameters, where decays into dark matter may or
may not contribute according to the mass of the scalar dark matter candidate.
1
Introduction
After the observation of an 125 GeV scalar particle at CERN-LHC by the ATLAS and CMS
collaborations [1, 2], the electroweak symmetry breaking mechanism has been experimentally
stablished. Now, one of the highest priorities of the LHC experiments is to measure precisely
the strenghts of the couplings of the Higgs boson to fermions and vector bosons [3], which
will allow to look for new states associated with the breaking symmetry mechanism in models
beyond the standard model (SM) [4]. In particular, family non-universal U (1)0 symmetry
models have many well-established motivations. For example, they provide hints to solve
the SM flavor puzzle [5], where regardless that all the fermions acquire masses at the same
∗
e-mail:
e-mail:
‡
e-mail:
§
e-mail:
¶
e-mail:
†
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
1
Mathematica and Fortran programs for various
analytic QCD couplings
arXiv:1411.1581v1 [hep-ph] 6 Nov 2014
1
C´
esar Ayala and Gorazd Cvetiˇ
c
Department of Physics, Universidad T´ecnica Federico Santa Mar´ıa, Casilla 110-V, Valpara´ıso,
Chile
E-mail: [email protected]
Abstract. We outline here the motivation for the existence of analytic QCD models, i.e.,
QCD frameworks in which the running coupling A(Q2 ) has no Landau singularities. The
analytic (holomorphic) coupling A(Q2 ) is the analog of the underlying pQCD coupling
a(Q2 ) ≡ αs (Q2 )/π, and any such A(Q2 ) defines an analytic QCD model. We present the
general construction procedure for the couplings Aν (Q2 ) which are analytic analogs of the
powers a(Q2 )ν . Three analytic QCD models are presented. Applications of our program
(in Mathematica) for calculation of Aν (Q2 ) in such models are presented. Programs in both
Mathematica and Fortran can be downloaded from the web page: gcvetic.usm.cl.
1. Why analytic QCD?
Perturbative QCD (pQCD) running coupling a(Q2 ) [≡ αs (Q2 )/π, where Q2 ≡ −q 2 ] has
<
unphysical (Landau) singularities at low spacelike momenta 0 < Q2 ∼ 1 GeV2 .
For example, the one-loop pQCD running coupling
a(Q2 )(1−`.) =
1
β0 ln(Q2 /Λ2Lan. )
(1)
has a Landau singularity (pole) at Q2 = Λ2Lan. (∼ 0.1 GeV2 ). The 2-loop pQCD coupling
a(Q2 )(2−`.) has a Landau pole at Q2 = Λ2Lan. and Landau cut at 0 < Q2 < Λ2Lan. .
It is expected that the true QCD coupling A(Q2 ) has no such singularities. Why?
General principles of QFT dictate that any spacelike observable D(Q2 ) (correlators of
currents, structure functions, etc.) is an analytic (holomorphic) function of Q2 in the entire Q2
2 ], where M
complex plane with the exception of the timelike axis: Q2 ∈ C\(−∞, −Mthr.
thr. ∼ 0.1
2
GeV is a threshold mass (∼ Mπ ). If D(Q ) can be evaluated as a leading-twist term, then it is a
function of the running coupling a(κQ2 ) where κ ∼ 1: D(Q2 ) = F(a(κQ2 )). Then the argument
a(κQ2 ) is expected to have the same analyticity properties as D, which is not the case with the
pQCD coupling in the usual renormalization schemes (MS, ’t Hooft, etc.).
2 ], represents an
A QCD coupling A(Q2 ) with holomorphic behavior for Q2 ∈ C\(−∞, −Mthr.
analytic QCD model (anQCD).
1
Preprint USM-TH-330. Based on the presentation given by G.C. at the 16th International workshop on
Advanced Computing and Analysis Techniques in physics research (ACAT 2014), Prague, Czech Republic,
September 1-5, 2014. To appear in the proceedings by the IOP Conference Series publishing.
APS/123-QED
A braid model for the particle X(3872)
C. Pe˜
na∗ and L. Jacak†
Institute of Physics, Wroclaw University of Technology,
Wyb. Wyspia´
nskiego 27, 50-370 Wrocaw, Poland
arXiv:1411.1574v1 [hep-ph] 6 Nov 2014
(Dated: November 7, 2014)
Abstract
The Model of Quark Exchange (MQE) describes the particle X(3872) as a molecule. We asked
whether braids influence the meson potential in the MQE. They are parameterized by a variable
t from the Burau’s representation. The present result shows that t rescales the coupling in the
meson potential determining if it is attractive or repulsive. As a consequence, a capture diagram
favored the molecular state for t = 0.85, it breaks for other values. For the future, braids may help
to study others exotic states in geometrical terms.
PACS numbers: 14.20.Pt, 03.65.Nk, 03.65.Fd
∗
[email protected]
†
[email protected]
1
A Phenomenological Model of the Glasma and Photon
Production∗
arXiv:1411.1548v1 [hep-ph] 6 Nov 2014
Larry McLerran(1,2,3)
1. Physics Department, Brookhaven National Laboratory, Upton, NY
11973, USA
2. RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973, USA
3. Physics Dept. Central China Normal University, Wuhan, China
I discuss a phenomenological model for the Glasma. I introduce over
occupied distributions for gluons, and compute their time evolution. I
use this model to estimate the ratio of quarks to gluons and the entropy
production as functions of time. I then discuss photon production at RHIC
and LHC, and how geometric scaling and the Glasma might explain generic
features of such production.
1. Introduction
There have been many talks at this meeting concerning the Color Glass
Condensate[1]-[5] and the Glasma[6]-[13], so I will not present an extended
review the subject in this talk. I will concentrate here on providing a simplified description of the evolution of the Glasma. The Glasma is a strongly
interacting Quark Gluon Plasma. It is not thermalized. It is produced very
shortly after the collision of two nuclei, thought of as sheets of Color Glass
Condensate, and evolves into the Thermalized Quark Gluon Plasma. The
Glasma is strongly interacting because the gluon distributiuons are over occupied, and this overoccupation enhances the interaction strength due to
Bose coherence. There may or may not be a Bose condensate of gluons
in the Glasma, but this interesting feature will not be the subject of this
talk[14]-[22]. In fact, I will ignore the possibility of such condensation when
I analyze the Glasma, although the result I present may be generalized to
the case where condensation is present.
∗
Invited talk presented at the 54’th Cracow School of Theoretical Physics, Zakopane,
Poland, June 2014
(1)
arXiv:1411.1495v1 [hep-ph] 6 Nov 2014
Pion, Kaon and Antiproton Production in P b + P b Collisions at
√
LHC Energy sNN = 2.76 TeV : A Model-based Analysis
P. Guptaroy1∗, S. Guptaroy2†
1
Department of Physics, Raghunathpur College,
P.O.: Raghunathpur 723133, Dist.: Purulia (WB), India.
2
Department of Physics, Basantidevi College,
147B Rashbehari Avenue, Kolkata 700029 India.
Abstract
Large Hadron Collider (LHC) had produced a vast amount of high precision data for
high energy heavy ion collision. We attempt here to study (i) transverse momenta spectra,
(ii) K/π, p/π ratio behaviours, (iii)rapidity distribution, and (iv) the nuclear modification
factors of the pion, kaon and antiproton produced in p + p and P b + P b collisions at energy
√
sN N = 2.76 TeV, on the basis of Sequential Chain Model (SCM). Comparisons of the
model-based results with the measured data on these observables are generally found to be
modestly satisfactory.
Keywords: Relativistic heavy ion collisions, baryon production, light mesons
PACS nos.: 25.75.-q, 13.60.Rj, 14.40.Be
∗
†
e-mail: [email protected] (Communicating author)
e-mail: [email protected]
1
ACFI-T14-15
Standard Model Nucleon EDM Revisited
Chien-Yeah Senga
a
Amherst Center for Fundamental Interactions
Department of Physics,
University of Massachusetts Amherst
arXiv:1411.1476v1 [hep-ph] 6 Nov 2014
Amherst, MA 01003 USA
(Dated: 5 November 2014)
Abstract
The Cabibbo-Kobayashi-Maskawa matrix in the Standard Model is currently the only
experimentally-confirmed source of CP-violation. The intrinsic electric dipole moment of the nucleon induced by this CP-phase via hadronic loop and pole diagrams has been studied more than
two decades ago, but the existing calculation is subject to various theoretical issues such as the
breakdown of chiral power counting and uncertainties in the determination of low energy constants.
We carry out an up-to-date re-analysis on both one-loop and pole diagram contributions to the
nucleon electric dipole moment based on Heavy Baryon Chiral Perturbation Theory in a way that
preserves power counting, and redo the determination of the low energy constants following the
results of more recent articles. Combined with an estimation of higher-order contributions, we
expect the long-distance contribution to the Standard Model nucleon electric dipole moment to be
approximately (1 × 10−32 − 6 × 10−32 )e cm.
PACS numbers: 13.40.Em,12.39.Fe
1
Upper bounds on sparticle masses
from muon g − 2 and the Higgs mass
and the complementarity of future colliders
arXiv:1411.1450v1 [hep-ph] 5 Nov 2014
Marcin Badziak1 , Zygmunt Lalak2 , Marek Lewicki3 , Marek Olechowski4 , Stefan Pokorski5
Institute of Theoretical Physics, Faculty of Physics, University of Warsaw
ul. Pasteura 5, PL–02–093 Warsaw, Poland
Abstract
Supersymmetric (SUSY) explanation of the discrepancy between the measurement of (g−2)µ
and its SM prediction puts strong upper bounds on the chargino and smuon masses. At the
same time, lower experimental limits on the chargino and smuon masses, combined with the
Higgs mass measurement, lead to an upper bound on the stop masses. The current LHC limits
on the chargino and smuon masses (for not too compressed spectrum) set the upper bound
on the stop masses of about 10 TeV. The discovery potential of the future lepton and hadron
colliders should lead to the discovery of SUSY if it is responsible for the explanation of the
(g − 2)µ anomaly. This conclusion follows from the fact that the upper bound on the stop
masses decreases with the increase of the lower experimental limit on the chargino and smuon
masses.
1
[email protected]
[email protected]
3
[email protected]
4
[email protected]
5
[email protected]
2
NUHEP-14/03
Lepton-Flavored Dark Matter
Jennifer Kile,1 Andrew Kobach,2 and Amarjit Soni3
1
arXiv:1411.1407v1 [hep-ph] 5 Nov 2014
Institute for Fundamental Theory, Department of Physics,
University of Florida, Gainesville, FL 32611, USA
2
Northwestern University, Department of Physics & Astronomy,
2145 Sheridan Road, Evanston, IL 60208, USA
3
Physics Department, Brookhaven National Laboratory, Upton, NY 11973 USA
(Dated: November 7, 2014)
In this work, we address two paradoxes. The first is that the measured dark-matter relic
density can be satisfied with new physics at O(100 GeV − 1 TeV), while the null results from
direct-detection experiments place lower bounds of O(10 TeV) on a new-physics scale. The
second puzzle is that the severe suppression of lepton-flavor-violating processes involving
electrons, e.g. µ → 3e, τ → eµµ, etc., implies that generic new-physics contributions to
lepton interactions cannot exist below O(10 − 100 TeV), whereas the 3.6σ deviation of the
muon g − 2 from the standard model can be explained by a new-physics scale < O(1 TeV).
Here, we suggest that it may not be a coincidence that both the muon g − 2 and the relic
density can be satisfied by a new-physics scale . 1 TeV. We consider the possibility of a
gauged lepton-flavor interaction that couples at tree level only to µ- and τ -flavored leptons
and the dark sector. Dark matter thus interacts appreciably only with particles of µ and τ
flavor at tree level and has loop-suppressed couplings to quarks and electrons. Remarkably,
if such a gauged flavor interaction exists at a scale O(100 GeV − 1 TeV), it allows for a
consistent phenomenological framework, compatible with the muon g − 2, the relic density,
direct detection, indirect detection, charged-lepton decays, and results from hadron and
e+ e− colliders. We suggest experimental tests for these ideas at colliders and for low-energy
observables.
PACS numbers: 95.35.+d, 11.30.Hv, 14.60.-z
I.
INTRODUCTION
In this work, we attempt to address two ongoing puzzles in particle physics. The first is that if
dark matter is a thermal relic, its annihilation cross section requires new physics at the electroweak
scale, i.e., in the range O(100 GeV − 1 TeV). However, the null results from direct-detection
experiments constrain that a new-physics scale between dark matter and nucleons must be > O(10
TeV) for a dark-matter mass & 10 GeV. This tension between the relic density and direct detection
may be pointing to the possibility that dark matter does not couple to quarks at tree level. Rather,
dark matter may couple primarily via interactions at the electroweak scale to other particles in
the standard model, e.g., leptons. If so, such a dark-matter candidate can satisfy the measured
relic density at tree level and accommodate the null results from direct detection by giving rise to
interactions between dark matter and quarks at the loop level.
If interactions at the electroweak scale exist between dark matter and leptons, then one generically expects such interactions between leptons themselves. There may be evidence for such an
interaction given that the current 3.6σ deviation of the muon g − 2 from the standard model value
could be explained by new interactions at a scale < O(1 TeV). However, the possible existence of
new physics at this scale introduces a second puzzle: interactions at such a scale do not manifest
themselves via other processes among charged leptons. For example, flavor-violating processes such
as µ → 3e, τ → eµµ, τ → eeµ, τ → 3e, µ → eγ [1] constrain new-physics scales to be > O(10−100
TeV). Additionally, flavor-conserving processes, such as lepton production at LEP, constrain new