1. science
2. physics

DarkSide-50: results from first argon run
Davide D’Angelo for the DarkSide collaboration
Universit`
a degli Studi di Milano e I.N.F.N., via Celoria 16, 20133 Milano, Italy
arXiv:1501.03541v1 [hep-ex] 15 Jan 2015
DOI: will be assigned
DarkSide (DS) at Gran Sasso underground laboratory is a direct dark matter search program based on TPCs with liquid argon from underground sources. The DS-50 TPC, with
50 kg of liquid argon is installed inside active neutron and muon detectors. DS-50 has been
taking data since Nov 2013, collecting more than 107 events with atmospheric argon. This
data represents an exposure to the largest background, beta decays of 39 Ar, comparable to
the full 3 y run of DS-50 with underground argon. When analysed with a threshold that
would give a sensitivity in the full run of about 10−45 cm2 at a WIMP mass of 100 GeV,
there is no 39 Ar background observed. We present the detector design and performance,
the results from the atmospheric argon run and plans for an upscale to a multi-ton detector
along with its sensitivity.
The DarkSide (DS) project [1] aims to direct Dark Matter detection via WIMP-nucleus scattering in liquid Argon. The detectors are dual phase Time Projection Chambers (TPCs) located
at Laboratori Nazionali del Gran Sasso in central Italy under a
rock coverage of ∼ 3800 m w.e. DS aims to a background-free exposure via three key concepts: (1) very low intrinsic background
levels, (2) discrimination of electron recoils and (3) active suppression of neutron background.
DS has a multi-stage approach: after the operation of a 10 kg
detector [2], we are now running DarkSide-50 (DS-50) detector
with a 45 kg fiducial mass TPC and a projected sensitivity of
∼ 10−45 cm2 for a 100 GeV WIMP. The project will continue with
a multi-ton detector and a sensitivity improvement of two orders
of magnitude.
The DS-50 TPC is depicted in Fig. 1. The scattering of
WIMPs or background in the active volume induces a prompt
scintillation light, called S1, and ionization. Electrons which do
not recombine are drifted by an electric field applied along the
z-axis. The maximum drift time across the 35.6 cm height is
∼ 375 µs at the operative field of 200 V/cm. Electrons are then
extracted into gaseous argon above the extraction grid, where Figure 1: DS-50 TPC prina secondary larger scintillation emission takes place, called S2. ciple of operation.
Two arrays of 19 3”-PMTs collect the light on each side of the
TPC.
PANIC14
1
arXiv:1501.03492v1 [astro-ph.CO] 14 Jan 2015
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, 2015
Direct Dark Matter Search with XENON100
S.E.A. Orrigo1 , a , b
on behalf of the XENON Collaboration
1
Department of Physics, University of Coimbra, Coimbra, Portugal
Abstract. The XENON100 experiment is the second phase of the XENON program for
the direct detection of the dark matter in the universe. The XENON100 detector is a
two-phase Time Projection Chamber filled with 161 kg of ultra pure liquid xenon. The
results from 224.6 live days of dark matter search with XENON100 are presented. No
evidence for dark matter in the form of WIMPs is found, excluding spin-independent
WIMP-nucleon scattering cross sections above 2 × 10−45 cm2 for a 55 GeV/c2 WIMP
at 90% confidence level (C.L.). The most stringent limit is established on the spindependent WIMP-neutron interaction for WIMP masses above 6 GeV/c2 , with a minimum cross section of 3.5 × 10−40 cm2 (90% C.L.) for a 45 GeV/c2 WIMP. The same
dataset is used to search for axions and axion-like-particles. The best limits to date are
set on the axion-electron coupling constant for solar axions, gAe < 7.7 × 10−12 (90%
C.L.), and for axion-like-particles, gAe < 1 × 10−12 (90% C.L.) for masses between 5 and
10 keV/c2 .
1 Introduction
Non-Barionic dark matter constitutes the 26.8 % of the total energy and the 84.5% of the total matter
of the known universe. The nature of the dark matter is among the fundamental open questions in
modern physics. One of the most favorite dark matter candidates are the Weakly Interacting Massive
Particle (WIMPs), cold and not-charged exotic relics of the Big Bang that interact with the ordinary
matter only through gravity and the weak interaction. Axions and Axion-Like Particles (ALPs) are
other well-motivated candidates for cold dark matter, introduced by many extensions of the Standard
Model of particle physics.
The XENON program aims at the direct detection of the dark matter in the universe using dualphase Time Projection Chambers (TPCs) of increasing sensitivity [1–3] filled with ultra pure liquid
xenon (LXe). All the XENON experiments are located underground at the Laboratori Nazionali del
Gran Sasso (LNGS) in Italy. The XENON100 experiment [2], having a total mass of 161 kg of LXe,
is the second phase of the program and has set the most stringent limits on the WIMP-nucleon spinindependent [4] and spin-dependent [5] cross sections and on the axion-electron coupling [6]. The
successor, XENON1T [3, 7], is a ton-scale TPC that will be commissioned in 2015 and it is expected
to improve the sensitivity by two orders of magnitude.
a Corresponding author e-mail: [email protected]
b Present address: IFIC, CSIC-Universidad de Valencia, E-46071 Valencia, Spain
Radiation tolerance of opto-electronic components proposed for space-based
quantum key distribution
Yue Chuan Tan∗ , Rakhitha Chandrasekara, Cliff Cheng and Alexander Ling
arXiv:1501.03595v1 [physics.ins-det] 15 Jan 2015
a
Centre for Quantum Technologies, National University of Singapore, Block S15, 3 Science Drive 2,
Singapore 117543
Plasma in low earth orbit can damage electronic components and potentially jeopardise the scientific
missions in space. Predicting the accumulated damage and understanding the components’ radiation
tolerance are important to mission planning. In this manuscript we report on the observed radiation tolerance of single photon detectors and a liquid crystal polarization rotator. We conclude that an uncooled
Si APD could continue to operate from more than a month up to beyond the lifetime of the satellite
depending on the orbit. The polarization rotator was also unaffected by the exposed dosage.
Keywords: quantum communication; space radiation; low earth orbit;
1.
Introduction
The requirement for line-of-sight transceiver locations limits the range of terrestrial free-space
optical quantum key distribution (QKD) [1] . This limitation may be overcome, hence establishing
a global QKD network by using satellites [2] in Low Earth Orbit (LEO) to transmit quantum
states of light through an optical link. For discrete variable QKD employing polarization entangled
photons, single photon sources and detectors can be carried on a satellite. The first step in this
direction is to demonstrate that the necessary opto-electronics components in a space-based QKD
network will operate in LEO. We have proposed that this can be performed cost-effectively with
nanosatellites called cubesats [3]. Cubesats in LEO (approximate altitude of 400 km) will be able
to survive for one year in orbit before falling back to Earth. We anticipate that one year is sufficient
time to carry out a proper space-based QKD demonstration.
The basic unit of a cubesat is a 10 cm cube (1U) with mass below one kilogram and with
typically 1.5 W of electrical power available [4]. Each 1U cube may be stacked into larger satellites
and typically are designed around commercial-off-the-shelf technologies. However, as the size and
mass available are limited, there is little room for adding shields against space radiation. It is
necessary to ensure that the opto-electronics devices in the experiment can operate reliably for the
expected lifetime of one year in LEO.
Space radiation in LEO consists of mainly protons and electrons trapped in the Earth’s magnetic
fields [5]. Proton induced damage is primarily displacement damage, while electrons tend to cause
ionizing damage. Both damage mechanisms result in degradation and operational failure of spacecraft electronics. For a space-based QKD experiment, the most radiation sensitive opto-electronic
devices are Si avalanche phototiodes (APDs) for detecting single photons and liquid crystal-based
polarization rotators (LCPR) used for selecting the polarization basis of the QKD measurements.
The target orbit for our proposed missions is at an altitude of about 400 km. More launch
opportunities are available at this altitude, including possible deployment via the International
Space Station (ISS). Furthermore, satellites at this altitude fall back to Earth within a year and so
there is no risk of long-term space debris from our proposed mission. To test the radiation tolerance
of the components, the target radiation environment was modeled using the Space Environment
Information System (SPENVIS) [6] with 2 mm of aluminium shielding assumed. The simulation
results from SPENVIS were used to determine the levels of irradiation for the test components. In
∗ Corresponding
author. Email: [email protected]
1
1
Performance of a Quintuple-GEM Based RICH
Detector Prototype
arXiv:1501.03530v1 [physics.ins-det] 14 Jan 2015
Marie Blatnik, Klaus Dehmelt, Abhay Deshpande, Dhruv Dixit, Nils Feege, Thomas K. Hemmick, Benji Lewis,
Martin L. Purschke, William Roh, Fernando Torales-Acosta, Thomas Videbæk, and Stephanie Zajac
ˇ
Abstract—Cerenkov
technology is one of the first choices
when it comes to particle identification in high energy particle
collision applications. Particularly challenging is the deployment
in the high pseudorapidity1 (forward) direction where particle
identification must allow for high lab momenta, up to about
ˇ
50 GeV/c. In this region Cerenkov
Ring-Imaging is among the
most viable solutions and will provide the desired performance
if the radiator has a low index of refraction, high yield of
photoelectrons, and allows precise measurement of the position
of each photoelectron. A RICH detector prototype based on
a novel concept that allows the use of a significantly shorter
radiator length compared to conventional RICH detectors has
been constructed and tested. The setup and the results obtained
are described.
ˇ
Index Terms—Cerenkov
detectors, RICH Detectors, Micropattern gas chambers, GEM detectors, Particle measurements,
Particle detectors, Nuclear physics instrumentation.
I. I NTRODUCTION
T
He Electron Ion Collider (EIC) [1], envisioned to be
constructed in the early 2020s will, for the first time,
precisely image the gluons and sea quarks in the proton and
nuclei. It will accelerate polarized electrons and a variety of
light and heavy ions, from H (p and d) to U , of which the
lightest ions can also be polarized. The EIC aims to completely
resolve the proton’s internal structure and explore a new QCD
frontier of ultra-dense gluon fields in nuclei at high energy. It
has been given highest priority2 of the U.S. QCD community
for new construction.
A detector capable of measuring the fragments of ElectronIon collisions has to overcome a number of challenges. The
particle flow is highly boosted into the forward direction due
to the beam kinematics, which creates a very high density of
particle tracks in the lab frame. A solution for Hadron particle
ˇ
identification (PID) is a Ring Imaging Cerenkov
(RICH)
detector with at least two radiators, with larger refraction index
for covering small(er) momenta and small refraction index for
covering the highest momentum range. The latter is usually
This manuscript was submitted for peer review on January 13, 2015.
This work was supported in part by the U.S. Department of Energy (DOE)
under award number 1901/59187.
M. Blatnik, K. Dehmelt, A. Deshpande, D. Dixit, N. Feege, T.K. Hemmick,
B. Lewis, W. Roh, F. Torales-Acosta, T. Videbæk, and S. Zajac are with the
Department of Physics and Astronomy, Stony Brook University, Stony Brook,
NY, 11794-3800 USA (e-mail: [email protected]).
M.L. Purschke is with Brookhaven National Lab, Upton, NY, 11973-5000
USA.
1 Spatial coordinate describing the angle of a particle relative to the beam
”
´ ¯ı
axis: η ” ´ln tan θ2
2 2014
Long-range plan, Joint Town Meetings on QCD, Temple University
achieved by using gas as radiator medium. However, the
amount of photoelectrons is limited due to the relatively small
number of single photons “produced” in the dilute medium.
A novel RICH concept has been developed and a detector
prototype tested as
1) proof-of-principle test in an electron-test-beam environment at SLAC ESTB3 and
2) under real-test conditions within a test-beam environment
with various hadrons at various momenta at FTBF4 .
In the following sections we describe the novel RICH
technology, the detector prototype setup, and the operation in
the test-beam facilities. Results from the tests will be described
and discussed.
II. N OVEL RICH TECHNOLOGY
For semi-inclusive and exclusive measurements in an EIC
detector particle identification will be a critical element. One
aims for hadron identification with better than 90% efficiency
and better than 95% purity. For higher momentum particles
(forward direction) one needs to achieve these measurements
to momenta of up to 50 GeV/c. Only low refractive index gasˇ
Cerenkov
detectors can operate in this regime.
A gas like Tetrafluoromethane CF4 has a very low index
of refraction, nr pλq ´ 1 „ 6.0 ˆ 10-4 for 140 nm [2] and
extraordinary high photon yield of more than 300 photons per
MeV [3].
ˇ
Cerenkov
light yield follows the relation [4][5]
ż
dλ
dNγ
2
“ 2πα sin θC
εpλq 2 ,
(1)
dx
λ
λmin
with εpλq as quantum efficiency, and one can see that the
largest photon yield per radiator length is dominated by
the smallest wavelengths. Consequently, Vacuum Ultraviolet
(VUV with 10 nm>λ>200 nm) photons in large number are
produced, which, however, provide a challenge for focusing
and conversion into photoelectrons.
For measuring the ring diameter of a charged particle traversing the radiator medium, with sufficient precision requires the
measurement of a sufficiently large number of photoelectrons.
ˇ
This in turn requires a sufficient number of Cerenkov
photons
produced in the radiator medium but also reflected from the
mirror.
To overcome this challenge two novel technologies have been
implemented in the presented RICH detector prototype setup:
3 End
Station (A) Test Beam
Test Beam Facility
4 Fermilab
X(3872), I G (J P C ) = 0+(1++), as the χ1c (2P ) charmonium
N.N. Achasov a
a
and E.V. Rogozina a,b
Laboratory of Theoretical Physics, Sobolev Institute
for Mathematics, 630090, Novosibirsk, Russia
arXiv:1501.03583v1 [hep-ph] 15 Jan 2015
b
Novosibirsk State University, 630090, Novosibirsk, Russia
(Dated: January 16, 2015)
Abstract
Reasons are given that X(3872), I G (J P C ) = 0+ (1++ ), is the χ1c (2P ) charmonium. Possibility
of verification of this assumption is discussed.
PACS numbers: 13.75.Lb, 11.15.Pg, 11.80.Et, 12.39.Fe
1
Charmed-strange mesons revisited: mass spectra and strong decays
Qin-Tao Song1,2,4 ,∗ Dian-Yong Chen1,2† ,‡ Xiang Liu2,3§ ,¶ and Takayuki Matsuki5,6∗∗
1
arXiv:1501.03575v1 [hep-ph] 15 Jan 2015
Nuclear Theory Group, Institute of Modern Physics of CAS, Lanzhou 730000, China
CS20141216 2 Research Center for Hadron and CSR Physics,
Lanzhou University & Institute of Modern Physics of CAS, Lanzhou 730000, China
3
School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China
4
University of Chinese Academy of Sciences, Beijing 100049, China
5
Tokyo Kasei University, 1-18-1 Kaga, Itabashi, Tokyo 173-8602, Japan
6
Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198, Japan
Inspired by the present experimental status of charmed-strange mesons, we perform a systematic study of the
charmed-strange meson family, in which we calculate the mass spectra of the charmed-strange meson family
by taking a screening effect into account in the Godfrey-Isgur model and investigate the corresponding strong
decays via the quark pair creation model. These phenomenological analyses of charmed-strange mesons not
only shed light on the features of the observed charmed-strange states, but also provide important information
on future experimental search for the missing higher radial and orbital excitations in the charmed-strange meson
family, which will be valuable task in LHCb, forthcoming BelleII and PANDA.
PACS numbers: 14.40.Lb, 12.38.Lg, 13.25.Ft
I.
INTRODUCTION
As experiments has largely progressed in the past decade,
more and more charmed-strange states have been reported [1].
Facing the abundant experimental observations, we need to
provide an answer, as one crucial task, to the question whether
these states can be identified in the charmed-strange meson
family, which is not only a valuable research topic relevant
to the underlying structure of the newly observed charmedstrange states, but is also helpful to establish the charmedstrange meson family step by step.
It is a suitable time to give a systematic study of the
charmed-strange meson family, which includes two main
topics, i.e., the mass spectrum and strong decay behavior.
At present, we have abundant experimental information of
charmed-strange states, which can be combined with the theoretical results to carry out the corresponding phenomenological study.
As the first key step of whole study of the charmed-strange
meson family, the investigation of the mass spectrum of
charmed-strange mesons should reflect how a charm quark
interacts with a strange antiquark. Godfrey and Isgur proposed the so-called Godfrey-Isgur (GI) model to describe the
interaction between q and q¯ quarks inside of mesons [2] some
thirty years ago. Although the GI model has achieved a great
success in reproducing/predicting the low lying mesons, there
exist some difficulties when reproducing the masses of higher
radial and orbital excitations, which is because the GI model
is a typical quenched model. A typical example of this defect appears in the low mass puzzle of D∗s0 (2317) [3–6] and
† Corresponding
author
§ Corresponding author
∗ Electronic address: [email protected]
‡ Electronic
address: [email protected]
¶ Electronic address: [email protected]
∗∗ Electronic address: [email protected]
D s1 (2460) [4–7], where the observed masses of D∗s0 (2317) and
D s1 (2460) are far lower than the corresponding results calculated using the GI model. A common feature of higher excitations is that they are near the thresholds of meson pairs,
which can interact with these higher excitations with the OZIallowed couplings. Hence, it is unsuitable to use the quenched
GI model to describe the mass spectrum of a higher excitated
meson and alternatively, we need to adopt an unquenched
model. Although there have been a couple of works studying
the heavy-light systems including charmed-strange mesons
together with their decay modes [8–15], in this work, we
would like to modify the GI model such that the screening
effect is introduced to reflect the unquenched pecularity. In
the following section, we present a detailed introduction of
the modified GI model.
In this work, we revisit the mass spectrum of the charmedstrange meson to apply the modified GI model , and compare our results with those of the former GI model and experimental data. We would like to see whether this treatment
improves the description of the charmed-strange meson spectrum to make the modified GI model reliable. We try further
to obtain information of wave functions of charmed-strange
mesons, which is important as an input in calculating the decay behavior of the two-body OZI-allowed decay of charmedstrange mesons.
Together with the study of the mass spectrum of charmedstrange mesons, it is a valuable information of the property
of charmed-strange mesons to investigate the decay behavior of charmed-strange mesons. We will adopt the quark
pair creation (QPC) model [16–22] to calculate the two-body
OZI-allowed decay of charmed-strange mesons, where the
corresponding partial and total decay widths are calculated.
Through this study, we can further test different possible assignments to the observed charmed-strange states. In addition,
we can predict the decay behavior of their partners, which are
still missing in experiment. This information is important for
experimentalists to further search for these missing charmedstrange mesons, which will be a main task in future experi-
The c¯
c interaction above threshold and the radiative decay X(3872) → J/ψγ
A.M. Badalian∗ and Yu.A. Simonov†
Institute of Theoretical and Experimental Physics, Moscow, Russia
B.L.G. Bakker‡
arXiv:1501.01168v1 [hep-ph] 6 Jan 2015
Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, The Netherlands
(Dated: January 7, 2015)
Radiative decays of X(3872) are studied in single-channel approximation (SCA) and in the
¯ ∗ are described with the string
coupled-channel (CC) approach, where the decay channels DD
3
˜
breaking mechanism. In SCA the transition rate Γ2 = Γ(2 P1 → ψγ) = 71.8 keV and large
˜ 1 = Γ(2 3 P1 → J/ψγ) = 85.4 keV are obtained, giving for their ratio the value R˜ψγ = Γ˜ 2 = 0.84.
Γ
˜1
Γ
In the CC approach three factors are shown to be equally important. First, the admixture of
the 1 3 P1 component in the normalized wave function of X(3872) due to the CC effects. Its
weight cX (ER ) = 0.200 ± 0.015 is calculated. Secondly, the use of the multipole function g(r)
instead of r in the overlap integrals, determining the partial widths. Thirdly, the choice of
the gluon-exchange interaction for X(3872), as well as for other states above threshold. If for
X(3872) the gluon-exchange potential is taken the same as for low-lying charmonium states, then
in the CC approach Γ1 = Γ(X(3872) → J/ψγ) ∼ 3 keV is very small, giving the large ratio
Rψγ = B(X(3872)→ψ(2S)γ)
≫ 1.0. Arguments are presented why the gluon-exchange interaction may
B(X(3872)→J/ψγ)
be suppressed for X(3872) and in this case Γ1 = 42.7 keV, Γ2 = 70.5 keV, and Rψγ = 1.65 are predicted for the minimal value cX (min) = 0.185, while for the maximal value cX = 0.215 we obtained
Γ1 = 30.8 keV, Γ2 = 73.2 keV, and Rψγ = 2.38, which agrees with the LHCb data.
PACS numbers: 11.10.St, 12.39.Pn, 12.40.Yx
I.
INTRODUCTION
In 2003 the Belle collaboration discovered the X(3872) as a narrow peak in the J/ψππ invariant mass distribution in
the decays B → J/ψππK [1]. Now its characteristics, like the mass, the strict restriction on the width, Γ <
∼ 1.2 MeV,
and the charge parity C = +, are well established [2–5]. In recent CDF and LHCb experiments the quantum
numbers of X(3872) were determined to be J P C = 1++ [6, 7]. Still, discussions about the nature of X(3872)
continue and to understand its exotic properties a special role is played by the radiative decays, X(3872) → J/ψγ
and X(3872) → ψ(3686)γ, which are sensitive to the behavior of the X(3872) wave function (w.f.) at medium and
large distances.
The first evidence for the decay X(3872) → J/ψγ was obtained by the Belle collaboration [8] and confirmed by the
BaBar collaboration [9]. Later BaBar has also observed the radiative decay X(3872) → ψ(3686)γ and determined the
branching ratio fraction Rψγ = B(X(3872)→ψ(3686)γ)
= 3.4 ± 1.4 [10]. However, Belle has not found evidence for the
B(X(3872)→J/ψγ)
radiative decay X(3872) → ψ(3686)γ and put an upper limit for the ratio [11],
Rψγ < 2.1.
(1)
Recently the LHCb group [12] has observed the decay X(3872) → ψ(3686)γ with a good statistics and determined
its value to be
Rψγ = 2.46 ± 0.64 ± 0.29,
(2)
¯ ψγ = 2.31 ± 0.57.
while in Ref. [13] the weighted average over three groups of measurements was determined to be R
Unfortunately, theoretical predictions for the partial widths Γ1 and Γ2 of the radiative decays X(3872) → J/ψγ
and X(3872) → ψ(3686)γ, respectively, vary widely in different models [14–22] (see also the recent reviews [23, 24]).
If X(3872) is considered as a pure 2 3 P1 charmonium state, then a large value Rψγ ≃ 5 is obtained as shown in
∗ Electronic
address: [email protected]
address: [email protected]
‡ Electronic address: [email protected]
† Electronic
Quark angular momentum in a spectator model
Tianbo Liua , Bo-Qiang Maa,b,c
a School
of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
b Collaborative Innovation Center of Quantum Matter, Beijing, China
c Center for High Energy Physics, Peking University, Beijing 100871, China
arXiv:1501.00062v2 [hep-ph] 6 Jan 2015
Abstract
We investigate the quark angular momentum in a model with the nucleon being a quark and a spectator. Both scalar and axialvector spectators are included. We perform the calculations in the light-cone formalism where the parton concept is well defined.
We calculate the quark helicity and canonical orbital angular momentum. Then we calculate the gravitational form factors which
are often related to the kinetic angular momentums, and find that even in a no gauge field model we cannot identify the canonical
angular momentums with half the sum of gravitational form factors. In addition, we examine the model relation between the orbital
angular momentum and pretzelosity, and find it is violated in the axial-vector case.
Keywords: proton spin, orbital angular momentum, gravitational form factor, pretzelosity
1. Introduction
Hadrons are bound states of the strong interaction which
is described by the quantum chromodynamics (QCD) in the
framework of Yang-Mills gauge field theory. One of the central
problems in particle physics is to determine nucleon structures
in terms of quark and gluon degrees of freedom. The decomposition of the proton spin is one of the most active frontiers
in recent years. Although the total angular momentum of an
isolated system is well defined, the decomposition to each constituent of a relativistic composite particle, such as the proton,
is non-trivial and of great interest.
The observation that only a small fraction [1, 2] (about 30%
in recent analysis [3, 4, 5]) of the proton spin is carried by
quark spins has puzzled the physics community for more than
two decades. This result severely deviates from the naive quark
model where the proton spin is from quark spins. Many possible ways to understand the “proton spin crisis” have been proposed, such as to attribute the remaining proton spin to the orbital angular momentum (OAM) and/or the gluon helicity. Due
to the Wigner rotation effect [6] which relates the spinors in
different frames, the constituent’s spin of a composite particle
in the rest frame can be decomposed into a spin part and a nonvanishing OAM in the infinite momentum frame (IMF) or lightcone formalism where the parton language is defined [7, 8, 9].
Therefore, the OAM plays an important role in understanding
the “proton spin puzzle”, although the gluon helicity also contributes a large fraction [10]. However, the decomposition of
proton spin, especially the definition of OAM, is still under controversy.
A most intuitive decomposition is to divide the proton
spin into quark spin, quark orbit, gluon spin and gluon orbit
Email addresses: [email protected] (Tianbo Liu), [email protected]
(Bo-Qiang Ma)
Preprint submitted to Physics Letters B
terms [11]:
1
,
2
where the quark orbit operator is defined as
S q + Lq + S g + Lg =
¯ + r × ∇ψ.
Lq = −iψγ
(1)
(2)
But the Lq , as well as S g and Lg , is not obviously gaugeinvariant and thus renders the physical meanings in common
situations obscure. To solve this problem, an explicitly gaugeinvariant decomposition is proposed [12]:
S q + L′q + Jg′ =
1
,
2
(3)
where each term is obviously gauge-invariant. It shares the
same definition for the quark spin operator in (1), but takes a
different definition for the quark orbit operator as
¯ + r × Dψ,
L′q = iψγ
(4)
where D = −∇ − ig A is the covariant derivative. In this decomposition, the total angular momentum for each parton flavor is
usually supposed to be related to the sum of two gravitational
form factors:
′
Jq/g
=
1
[Aq/g (0) + Bq/g (0)],
2
(5)
where the two form factors A and B can be measured through
the deeply virtual Compton scattering (DVCS) process.
Recently, Chen et al. revived the idea to decompose the
gauge potential Aµ into a pure gauge term Apure
µ , which plays
the role on gauge symmetry and only has to do with unphysphy
ical degrees of freedom, and a physical term Aµ , which involves the two physical degrees of freedom [13, 14]. With
this approach, many more decomposition versions were proposed [15, 16, 17]. As observed in [18] and discussed in details
January 7, 2015
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)
arXiv:1501.03555v1 [hep-ex] 15 Jan 2015
CERN-PH-EP-2014-278
Submitted to: JHEP
Search for squarks and gluinos in events with isolated leptons,
√
jets and missing transverse momentum at s = 8 TeV with the
ATLAS detector
The ATLAS Collaboration
Abstract
The results of a search for supersymmetry in final states containing at least one isolated lepton
(electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large
Hadron Collider are reported. The search is based on proton–proton collision data at a centre-of-mass
√
energy s = 8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1 . No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric
particle masses for various supersymmetric models. Depending on the model, the search excludes
gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/Rc = 950
GeV for a cut-off scale times radius (ΛRc ) of approximately 30.
c 2015 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.
January 16, 2015 1:27 WSPC/INSTRUCTION FILE
basilvac
arXiv:1501.03749v1 [astro-ph.CO] 15 Jan 2015
Modern Physics Letters A
c World Scientific Publishing Company
Cosmic expansion and structure formation in running vacuum
cosmologies
Spyros Basilakos∗
Research Center for Astronomy and Applied Mathematics, Academy of Athens
Soranou Efesiou 4, 11527, Athens, Greece
[email protected]
We investigate the dynamics of the FLRW flat cosmological models in which the vacuum
energy varies with redshift. A particularly well motivated model of this type is the socalled quantum field vacuum, in which both kind of terms H 2 and constant appear in the
effective dark energy density affecting the evolution of the main cosmological functions
at the background and perturbation levels. Specifically, it turns out that the functional
form of the quantum vacuum endows the vacuum energy of a mild dynamical evolution
which could be observed nowadays and appears as dynamical dark energy. Interestingly,
the low-energy behavior is very close to the usual ΛCDM model, but it is by no means
identical. Finally, within the framework of the quantum field vacuum we generalize the
large scale structure properties, namely growth of matter perturbations, cluster number
counts and spherical collapse model.
Keywords: Cosmology; Dark Energy; Large Scale Structure.
PACS Nos.: 98.80.-k, 95.35.+d, 95.36.+x
1. Introduction
The statistical analysis of various cosmological data (SNIa, Cosmic Microwave
Background-CMB, Baryonic Acoustic Oscillations-BAOs, Hubble parameter measurements etc) strongly suggests that we live in a spatially flat universe that consists
of ∼ 4% baryonic matter, ∼ 26% dark matter and ∼ 70% some sort of dark energy
(hereafter DE) which is necessary to explain the accelerated expansion of the universe (see Refs.[1, 2] and references therein). Although there is a common agreement
regarding the ingredients of the universe, there are different views concerning the
possible physical mechanism which is responsible for the cosmic acceleration.
The simplest dark energy candidate corresponds to a cosmological constant. In
the standard concordance ΛCDM model, the overall cosmic fluid contains baryons,
cold dark matter plus a vacuum energy (cosmological constant), that appears to fit
accurately the current observational data and thus provides an excellent scenario to
describe the observed universe. However, the concordance model suffers from, among
other, two fundamental problems: (a) The fine tuning problem i.e., the fact that
∗ email:
[email protected]
1
Prepared for submission to JHEP
DESY 15-008,CP3-Origins-2015-004 DNRF90,
DIAS-2015-4
arXiv:1501.03734v1 [hep-lat] 15 Jan 2015
First moment of the flavour octet nucleon parton
distribution function using lattice QCD
Constantia Alexandroua,b Martha Constantinoua Simon Dinterc Vincent Drachd
Kyriakos Hadjiyiannakoua Karl Jansena,b,c Giannis Koutsoua Alejandro Vaqueroa
a
Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
Computation-based Science and Technology Research Center (CaSToRC), The Cyprus Institute,20
Constantinou Kavafi Street Nicosia 2121, Cyprus
c
NIC, DESY, Platanenallee 6, D-15738 Zeuthen, Germany
d
CP 3 -Origins & the Danish Institute for Advanced Study DIAS, University of Southern Denmark,
Campusvej 55, DK-5230 Odense M, Denmark
b
E-mail: [email protected], [email protected]
Abstract: We perform a lattice computation of the flavour octet contribution to the
(8)
average quark momentum in a nucleon, hxiµ2 =4 GeV2 . In particular, we fully take the
disconnected contributions into account in our analysis for which we use a generalization
of the technique developed in [1]. We investigate systematic effects with a particular
emphasis on the excited states contamination. We find that in the renormalization free
hxi(3)
(3) the non-singlet moment) the excited state contributions cancel to a
ratio hxi
(8) (with hxi
large extend making this ratio a promising candidate for a comparison to phenomenological
analyses. Our final result for this ratio is in agreement with the phenomenological value
hxi(3)
and we find, including systematic errors, hxi
(8) = 0.39(1)(4).
Keywords: parton distribution function,lattice QCD
arXiv:1501.03722v1 [nucl-th] 15 Jan 2015
The hypercentral Constituent Quark Model and
its application to baryon properties
M.M. Giannini
Dipartimento di Fisica dell’Universit`a di Genova
and
I.N.F.N., Sezione di Genova
E. Santopinto
I.N.F.N., Sezione di Genova
Abstract
The hypercentral Constituent Quark Model (hCQM) for the baryon
structure is reviewed and its applications are systematically discussed.
The model is based on a simple form of the quark potential, which contains a Coulomb-like interaction and a confinement, both expressed in
terms of a collective space coordinate, the hyperradius. The model has
only three free parameters, determined in order to describe the baryon
spectrum. Once the parameters have been fixed, the model, in its non
relativistic version, is used to predict various quantities of physical interest, namely the elastic nucleon form factors, the photocouplings and
the helicity amplitudes for the electromagnetic excitation of the baryon
resonances. In particular, the Q2 dependence of the helicity amplitude is
quite well reproduced, thanks to the Coulomb-like interaction. The model
is reformulated in a relativistic version by means of the Point Form hamilton dynamics. While the inclusion of relativity does not alter the results
for the helicity amplitudes, a good description of the nucleon elastic form
factors is obtained.
Contents
1 Introduction
2
2 A review of Consituent Quark Models
2.1 Non relativistic approach . . . . . . .
2.2 The Isgur-Karl model . . . . . . . . .
2.3 The Capstick-Isgur model . . . . . . .
2.4 The U(7) model . . . . . . . . . . . . .
2.5 The Goldstone Boson Exchange Model
2.6 The Bonn model . . . . . . . . . . . .
2.7 The interacting quark-diquark model .
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G-Bounce Inflation: Towards Nonsingular Inflation Cosmology with Galileon Field
Taotao Qiu1,2∗ and Yu-Tong Wang3†
arXiv:1501.03568v1 [astro-ph.CO] 15 Jan 2015
1 Institute of Astrophysics, Central China Normal University, Wuhan 430079, China
2 State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,
Chinese Academy of Sciences, Beijing 100190, China and
3 School of Physics, University of Chinese Academy of Sciences, Beijing 100049, China
We study a nonsingular bounce inflation model, which can drive the early universe from a contracting phase, bounce into an ordinary inflationary phase, followed by the reheating process. Besides the
bounce that avoided the Big-Bang singularity which appears in the standard cosmological scenario,
we make use of the Horndesky theory and design the kinetic and potential forms of the lagrangian,
so that neither of the two big problems in bouncing cosmology, namely the ghost and the anisotropy
problems, will appear. The cosmological perturbations can be generated either in the contracting
phase or in the inflationary phase, where in the latter the power spectrum will be scale-invariant
and fit the observational data, while in the former the perturbations will have nontrivial features
that will be tested by the large scale structure experiments. We also fit our model to the CMB TT
power spectrum.
I.
INTRODUCTION
The standard model of cosmology regards inflation [1–6] as an important period in the early universe. As a superfast expansion after the Big Bang, the inflation can solve a series of cosmological problems such as horizon , flatness,
monopole and so on, as well as give rise to scale-invariant scalar perturbations that can fit with the data. However,
traditional inflation scenario still needs to be improved, because of the so-called “singularity problem” which was
proposed by Hawking et al. in their early work of singularity theorem [7, 8]. According to their proof to this theorem,
if we track back inflation to its very beginning, we will generally meet the singularity of the early universe (the BigBang singularity). At the singularity, everything blows up and one can not get control of the universe under classical
description. Since the singularity occurs before the onset of inflation, it can hardly be solved within inflation scenario
itself. This motivates us to find alternative theories in pre-inflation era.
Phenomenologically, there might be quite a few evolutions that can be set in front of inflation in order to get
rid of this problem. As an example, the universe may undergo a contracting phase where the scale factor a(t)
shrinks initially and then, by some mechanism, “bounces” into an expanding one [9]. The whole process can be done
non-singularly if at the bouncing point aB (t) 6= 0 [10]. The bouncing scenario has many interesting properties, for
example, the Big-Bang puzzles such as horizon problem and flatness problem can be solved even in contracting phase,
and scale-invariant primordial perturbations can be generated, etc [11]. Moreover, such non-singular scenario can also
be non-trivially extended to the cyclic universe [12, 13].
In bouncing inflation scenario however, there will be two more latent problems. One of them is the so-called “ghost
instability”. This problem claims that field theory models that violates the Null Energy Condition (NEC) will generally
give rise to “ghost” degrees of freedom, which causes the instability. The problems is originated from the “Ostradski
problem” [14] in field theory, and the first cosmological application of this problem was on dark energy models [15].
Since a nonsingular bounce violates NEC, normally the ghost will appear. However, recently an interesting “Galileon”
theories [16, 17] has been shown to be able to avoid such ghost degree of freedom while violating NEC (see pioneering
work on such kind of models in [18]). The reason is that although Galileons have higher derivative operators that
can violate NEC, due to the delicate design of the Lagrangian, there will only be one dynamical degree of freedom,
which can be made normal. The other degrees of freedom is non-dynamical, thus will not lead to any instabilities.
Therefore, in this paper we will make use of Galileon theory to build our model. Note that pure Galileon bounce
models has also been proposed in the literatures [19, 20], which can avoid ghost instability on NEC violation.
The other problem is known as “anisotropy problem” [21], which will impose additional constraint on the evolution
of the universe before the bounce. An exact isotropic universe at the initial time needs somehow fine-tuning, so in
realistic models of the early universe, certain amount of anisotropies will exist. In pure inflation scenario, this will
not be a problem because the anisotropies will decay in expanding universe, and will eventually be diluted away by
∗ Electronic
† Electronic
address: [email protected]
address: [email protected]
High Energy Physics Signatures from Inflation
and Conformal Symmetry of de Sitter
A. Kehagiasa,b and A. Riottob
arXiv:1501.03515v1 [hep-th] 14 Jan 2015
a
b
Physics Division, National Technical University of Athens,
15780 Zografou Campus, Athens, Greece
Department of Theoretical Physics and Center for Astroparticle Physics (CAP)
24 quai E. Ansermet, CH-1211 Geneva 4, Switzerland
Abstract
During inflation, the geometry of spacetime is described by a (quasi-)de Sitter phase. Inflationary observables are determined by the underlying (softly broken) de Sitter isometry group SO(1, 4) which acts
like a conformal group on R3 : when the fluctuations are on super-Hubble scales, the correlators of the
scalar fields are constrained by conformal invariance. Heavy fields with mass m larger than the Hubble
rate H correspond to operators with imaginary dimensions in the dual Euclidean three-dimensional conformal field theory. By making use of the dS/CFT correspondence we show that, besides the Boltzmann
suppression expected from the thermal properties of de Sitter space, the generic effect of heavy fields in
the inflationary correlators of the light fields is to introduce power-law suppressed corrections of the form
O(H 2 /m2 ). This can be seen, for instance, at the level of the four-point correlator for which we provide
the correction due to a massive scalar field exchange.
BOW-PH-160
arXiv:1501.03500v1 [hep-th] 14 Jan 2015
CHY representations for gauge theory and gravity amplitudes
with up to three massive particles
Stephen G. Naculich1
Department of Physics
Bowdoin College
Brunswick, ME 04011, USA
[email protected]
Abstract
We show that a wide class of tree-level scattering amplitudes involving scalars,
gauge bosons, and gravitons, up to three of which may be massive, can be expressed in
terms of a Cachazo-He-Yuan representation as a sum over solutions of the scattering
equations. These amplitudes, when expressed in terms of the appropriate kinematic
invariants, are independent of the masses and therefore identical to the corresponding
massless amplitudes.
1
Research supported in part by the National Science Foundation under Grant No. PHY14-16123.
Semiclassical corrections to black hole entropy and the generalized uncertainty
principle
Pedro Bargue˜
no∗
Departamento de F´ısica, Universidad de los Andes,
Apartado A´ereo 4976, Bogot´
a, Distrito Capital, Colombia
Elias C. Vagenas†
arXiv:1501.03256v1 [hep-th] 14 Jan 2015
Theoretical Physics Group, Department of Physics,
Kuwait University, P.O. Box 5969, Safat 13060, Kuwait
In this paper, employing the path integral method in the framework of a canonical description of
a Schwarzschild black hole, we obtain the corrected inverse temperature and entropy of the black
hole. The corrections are those coming from the quantum effects as well as from the Generalized
Uncertainty Principle effects. Furthermore, an equivalence between the polymer quantization and
the Generalized Uncertainty Principle description is shown provided the parameters characterizing
these two descriptions are proportional.
I.
INTRODUCTION
After Mead [1], who was the first who pointed out the
role of gravity on the existence of a fundamental measurable length, a considerably amount of effort has been devoted to study the modification of the Heisenberg uncertainty principle, known as Generalized Uncertainty Principle (GUP), together with the consequences it leads to
[2–18]. A specific form of the GUP and its associated
commutation relations, together with its physical consequences have been recently studied [19, 20] 1 . Moreover,
there has been a very recent interest in a different version
of the GUP [27–29], which predicts not only a minimum
length but also a maximum momentum [14–16].
As shown in [19], the effects of this GUP can be implemented both in classical and quantum systems by defining deformed commutation relations by means of
(1)
xi = x0i ; pi = p0i 1 − αp0 + 2α2 p20 ,
P
3
where [x0i , p0j ] = i~δij and p20 =
j=1 p0j p0j and
α = α0 /mp c, being α0 a dimensionless constant. Interestingly, the fact that polymer quantization leads to a
modified uncertainty principle [10] has led some authors
to think that some forms of GUPs and polymer quantization predict the same physics [30].
Among all quantum gravitational effects one can think
of, black hole (BH) entropy can be considered as the
paradigmatic one. From the realization that BHs are
thermodynamic objects [31–33] which radiate [34, 35],
the entropy of a Schwarzschild BH is given by the
Bekenstein–Hawking relation
SBH =
∗
†
1
ABH
,
4lp2
(2)
[email protected]
[email protected]
It is noteworthy that since there is a plethora of different forms of
GUP, the phenomenological implications of GUP are numerous
[21–26] .
q
where ABH is the area of the BH horizon and lp = G~
c3
is the Planck length. After these findings, several approaches to quantum gravity (QG) have predicted the
following form for the QG-corrected BH entropy [36–47]
SQG
ABH
=
+ c0 ln
k
4lp2
ABH
4lp2
+
∞
X
n=1
cn
ABH
4lp2
−n
, (3)
where the cn coefficients are model–dependent parameters. Specifically, loop quantum gravity calculations are
used to fix c0 = −1/2 [48].
In particular, the deformed commutation relations previously presented have been widely used to compute the
effects of the GUP on the BH entropy from different perspectives (see, for example, [39, 49–52]), which reads
s
√
πα0 ABH πα20
SGUP
ABH
ABH
+O(lp3 ).
=
+
−
ln
k
4lp2
4
4lp2
64
4lp2
(4)
Therefore, both the logarithmic correction√(with the correct sign) and a new term with goes as ABH can be
derived employing GUP.
The paper is organized as follows. In section II,
we briefly present how to include quantum effects on
the inverse temperature as well as the entropy of the
Schwarzschild BH by means of the path integral method
which is applied to a canonical description of the BH
[53]. Using this semiclassical approach, the logarithmic
correction in the entropy is also obtained [53]. In section III, following the procedure described in section II,
GUP effects as well as quantum effects are included [54],
thus the expressions for the corresponding corrected inverse temperature and entropy of the Schwarzschild BH
are obtained. In section IV, an equivalence between the
polymer quantization and the GUP description is pointed
out provided that the parameters that characterize these
two descriptions are proportional. Finally, in section V,
a brief summary of the obtained results is given.
Thawing quintessence from the inflationary epoch to today
Gaveshna Gupta,1, ∗ Raghavan Rangarajan,1, † and Anjan A. Sen2, ‡
arXiv:1412.6915v1 [astro-ph.CO] 22 Dec 2014
2
1
Physical Research Laboratory, Navrangpura, Ahmedabad, 380009, India
Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi 110025, India
(Dated: December 23, 2014)
By considering observational constraints from the recent Union2.1 Supernova type Ia data, the
baryon acoustic oscillations data, the cosmic microwave background shift parameter measurement
by Planck and the observational Hubble parameter H(z) data we obtain a lower bound on the initial
value of the quintessence field in thawing quintessence models of dark energy. For potentials of the
form V (φ) ∼ φ±2 we find that the initial value φi > 7 × 1018 GeV. We then relate φi to the duration
of inflation by assuming that the initial value of the quintessence field is determined by quantum
fluctuations of the quintessence field during inflation. From the lower bound on φi we obtain a lower
bound on the number of e-foldings of inflation, namely, N > 2 × 1011 .
PACS numbers:
I.
INTRODUCTION
Cosmological observations [1] [2] [3] of the past one and
a half decades indicate that the Universe is undergoing
accelerated expansion. Although a non-zero cosmological constant can explain the current acceleration of the
Universe, one still has to explain why it is so small and
why only at recent times it has started to dominate the
energy density of the Universe [4]. These issues have motivated the exploration of alternative theories to explain
the late time acceleration as due to a source of energy referred to as dark energy [5] [6]. A quintessence model is
one amongst such theories where the dark energy arises
from a scalar field φ rolling slowly down a potential.
The equation of state parameter w can be defined as
the ratio of the pressure to the energy density
w = p/ρ.
(1)
A cosmological constant is equivalent to w = −1 whereas
a quintessence field generates a time dependent equation
of state w(t) > −1. Caldwell and Linder [7] showed that
the quintessence models in which the scalar field rolls
down its potential towards a minimum can be classified
into two categories, namely freezing and thawing models, with quite different behavior. In thawing models at
early times the field gets locked at a value away from the
minimum of the potential due to large Hubble damping.
At late times when Hubble damping diminishes, the field
starts to roll down towards the minimum. These models
have a value of w which begins near −1 and gradually
increases with time. In freezing models the field rolls towards its potential minimum initially and slows down at
late times as it comes to dominate the Universe. These
models have a value of w which decreases with time. In
both cases w ≈ −1 around the present epoch. Thawing
∗ Electronic
address: [email protected]
† Electronic address: [email protected]
‡ Electronic address: [email protected]
models with a nearly flat potential provide a natural way
to produce a value of w that stays close to, but not exactly equal to −1. The field begins with w ≈ −1 at high
redshifts, and w increases only slightly by low redshifts.
These models depend on initial field values (in contrast
with freezing models of quintessence).
In the present work we evaluate the cosmological consequences of the evolving quintessence field by considering various observational datasets and obtain plausible
initial values of the scalar field φi in the context of thawing models. The bound on the the allowed values of φi
has been previously obtained in Ref. [8]. Our current
numerical analysis provides stronger constraints on φi .
We then relate the initial value to quantum fluctuations
of φ during inflation and thereby to the duration of inflation. Our work in this article is organised as follows.
In section II we describe the thawing quintessence model
in the standard minimal framework. In section III we
provide a detailed description of the datasets used to obtain the observational constraints on the parameters of
the model. In section IV we use the results obtained in
our investigation to obtain a lower bound on the initial
value of φ. We then discuss the generation of the initial
value by quantum fluctuations during inflation and use
the lower bound on φi to obtain a lower bound on the
number of e-foldings of inflation, N . We end with our
conclusions in section V.
II.
THE THAWING QUINTESSENCE
SCENARIO
We will assume that the dark energy is provided by
a minimally coupled scalar field φ with the equation of
motion for the homogeneous component given by
dV
φ¨ + 3H φ˙ +
= 0,
dφ
where the Hubble parameter H is given by
q
a˙
= ρ/3Mp2 .
H=
a
(2)
(3)
Prepared for submission to JHEP
FTUAM-15-2
IFT-UAM/CSIC-15-004
KIAS-P15003
arXiv:1501.03799v1 [hep-ph] 15 Jan 2015
Resonant Higgs boson pair production in the
hh → b¯
b W W → b¯
b`+ν`−ν
¯ decay channel
V´ıctor Mart´ın Lozano,a,b Jes´
us M. Morenoa and Chan Beom Parkc,d
a
Instituto de F´ısica Te´
orica, IFT-UAM/CSIC, Nicol´
as Cabrera 13,
UAM Cantoblanco, 28049 Madrid, Spain.
b
Dept. F´ısica Te´
orica, Universidad Aut´
onoma de Madrid, 28049 Madrid, Spain.
c
Korea Institute for Advanced Study, Seoul 130–722, Korea.
d
CERN, Theory Division, 1211 Geneva 23, Switzerland.
E-mail: [email protected], [email protected],
[email protected]
Abstract: Adding a scalar singlet provides one of the simplest extensions of the Standard
Model. In this work we briefly review the latest constraints on the mass and mixing of
the new Higgs boson and study its production and decay at the LHC. We mainly focus
on double Higgs production in the hh → b¯bW W → b¯b`+ ν`− ν¯ decay channel. This decay
is found to be efficient in a region of masses of the heavy Higgs boson of 260 – 500 GeV,
so it is complementary to the 4b channel, more efficient for Higgs bosons having masses
greater than 500 GeV. We analyse this di-leptonic decay channel in detail using kinematic
variables such as MT2 and the MT2 -assisted on-shell reconstruction of invisible momenta.
Using proper cuts, a significance of ∼ 3σ for 3000 fb−1 can be achieved at the 14 TeV LHC
for mH = 260 – 400 GeV if the mixing is close to its present limit and BR(H → hh) ≈ 1.
Smaller mixing values would require combining various decay channels in order to reach
a similar significance. The complementarity among H → hh, H → ZZ and H → W W
channels is studied for arbitrary BR(H → hh) values.
Keywords: Higgs physics, Beyond Standard Model, Hadron-Hadron Scattering, Particle
and resonance production
A Simple Motivated Completion of the Standard Model below the Planck Scale:
Axions and Right-Handed Neutrinos
Alberto Salvio
Departamento de F´ısica Te´orica, Universidad Aut´onoma de Madrid
and Instituto de F´ısica Te´orica IFT-UAM/CSIC, Madrid, Spain.
arXiv:1501.03781v1 [hep-ph] 15 Jan 2015
Report number: IFT-UAM/CSIC-15-003
Abstract
We study a simple Standard Model (SM) extension, which includes three families of right-handed neutrinos with generic
non-trivial flavor structure and an economic implementation of the invisible axion idea. We find that in some regions of the
parameter space this model accounts for all experimentally confirmed pieces of evidence for physics beyond the SM: it explains
neutrino masses (via the type-I see-saw mechanism), dark matter, baryon asymmetry (through leptogenesis), solve the strong
CP problem and has a stable electroweak vacuum. The last property allows us to identify the Higgs field with the inflaton.
Keywords: Higgs, vacuum stability, axions, right-handed neutrinos, cosmic inflation
1. Introduction
Although no unambiguous signal of physics beyond the
SM (BSM) has appeared so far at the LHC, there is no
doubt that the SM has to be extended. Neutrino oscillations,
which leads to the existence of small (left-handed) neutrino
masses, and the observational evidence for dark matter (DM)
is enough to state that the SM is incomplete.
Other unsatisfactory features of the SM are an insufficient
baryon asymmetry of the universe, the strong CP, gauge hierarchy and cosmological constant problems.
Moreover, precision calculations [1, 2] indicate that the
SM potential develops an instability at a scale of the order of
1010 GeV, for central measured values of the SM parameters.
This is not particularly worrisome per se because the probability of tunneling to the absolute minimum, where life is
impossible, is spectacularly small [1]. However, it may lead
to some issues during the exponential expansion of the early
universe (inflation) [3, 4, 5]. Moreover, the (absolute) stability up to the Planck scale MPl essentially guarantees that one
can trigger inflation through the Higgs field [6, 7, 8, 9], linking particle physics and cosmology: this is interesting because it leads to relations between particle physics and cosmological observables. The presence of such an instability
in the SM is not firmly confirmed because of non-negligible
uncertainties on the top mass and the QCD gauge coupling;
but, if confirmed, it would suggests that heavy right-handed
neutrinos (at scales suitable for the see-saw mechanism and
Preprint submitted to the arXiv
thermal leptogenesis) and the physics of the (QCD) axion
may be relevant for the issue of the electroweak (EW) vacuum instability and therefore inflation.
The aim of this paper is to identify a simple and wellmotivated model where the following signals of BSM physics
can all be addressed and which adds to the SM only righthanded neutrinos and the extra fields needed to implement
the axion idea:
1. Small neutrino masses. We adopt the perhaps simplest
explanation: the type-I see-saw mechanism based on
right-handed neutrinos. The addition of right-handed
neutrinos also symmetrize the field content of the SM
giving to each SM left-handed particle a right-handed
counterpart.
2. Dark matter. As a DM candidate we consider the
axion [10], a light spin-0 particle whose existence is
implied by the spontaneous symmetry breaking of a
U(1) symmetry, the Peccei-Quinn (PQ) symmetry [11]
that explains why strong interactions do not violate CP.
In particular, we consider the invisible axion model
proposed by Kim, Shifman, Vainshtein and Zakharov
(KSVZ) [12], which has a simple structure and a small
number of free parameters.
3. Baryon asymmetry. It can be generated through (thermal) leptogenesis [13], which is implemented with the
same right-handed neutrinos that allow the light neutrinos to have masses.
January 16, 2015
arXiv:1501.03754v1 [hep-ph] 15 Jan 2015
Prepared for submission to JHEP
Resummation of non-global logarithms and
the BFKL equation
Simon Caron-Huot
a
Niels Bohr International Academy and Discovery Center, Blegdamsvej 17, Copenhagen 2100, Denmark
E-mail: [email protected]
Abstract: We consider a ‘color density matrix’ in gauge theory. We argue that it systematically resums large logarithms originating from wide-angle soft radiation, sometimes referred
to as non-global logarithms, to all logarithmic orders. We calculate its anomalous dimension
at leading- and next-to-leading order. Combined with a conformal transformation known to
relate this problem to shockwave scattering in the Regge limit, this is used to rederive the
next-to-leading order Balitsky-Fadin-Kuraev-Lipatov equation (including its nonlinear generalization, the so-called Balitsky-JIMWLK equation), finding perfect agreement with the
literature. Exponentiation of divergences to all logarithmic orders is demonstrated. The
possibility of obtaining the evolution equation (and BFKL) to three-loop is discussed.
Keywords: Resummation, forward physics, effective field theories.
Prepared for submission to JCAP
arXiv:1501.03729v1 [hep-ph] 15 Jan 2015
Form factors for dark matter capture
by the Sun in effective theories
Riccardo Catenaa and Bodo Schwabea
a Institut
f¨
ur Theoretische Physik, Friedrich-Hund-Platz 1, 37077 G¨ottingen, Germany
E-mail: [email protected],
[email protected]
Abstract. In the effective theory of isoscalar and isovector dark matter-nucleon interactions
mediated by a heavy spin-1 or spin-0 particle, 8 isotope-dependent nuclear response functions
can be generated in the dark matter scattering by nuclei. We compute the 8 nuclear response
functions for the 16 most abundant elements in the Sun, i.e. H, 3 He, 4 He, 12 C, 14 N, 16 O, 20 Ne,
23 Na, 24 Mg, 27 Al, 28 Si, 32 S, 40 Ar, 40 Ca, 56 Fe, and 59 Ni, through detailed numerical shell model
calculations. We use our response functions to compute the rate of dark matter capture by the
Sun for all isoscalar and isovector dark matter-nucleon effective interactions, including several
operators previously considered for dark matter direct detection only. We study in detail the
dependence of the capture rate on specific dark matter-nucleon interaction operators, and on
the different elements in the Sun. We find that a so far neglected momentum dependent dark
matter coupling to the nuclear vector charge gives a larger contribution to the capture rate
than the constant spin-dependent interaction commonly included in experimental searches.
Our investigation lays the foundations for model independent analyses of dark matter induced
neutrino signals from the Sun. The nuclear response functions obtained in this study are listed
in analytic form in an appendix, ready to be used in other projects.
Keywords: dark matter theory, dark matter experiments
Wigner Distributions for Gluons in Light-front Dressed Quark
Model
Asmita Mukherjee, Sreeraj Nair and Vikash Kumar Ojha
Department of Physics,
Indian Institute of Technology Bombay,
arXiv:1501.03728v1 [hep-ph] 15 Jan 2015
Powai, Mumbai 400076, India.
(Dated: January 16, 2015)
Abstract
We present a calculation of Wigner distributions for gluons in light-front dressed quark model. We
calculate the kinetic and canonical gluon orbital angular momentum and spin-orbit correlation of the
gluons in this model.
1
HRI-RECAPP-2014-016
Dark matter, neutrino masses and high scale validity of an inert
Higgs doublet model
arXiv:1501.03700v1 [hep-ph] 15 Jan 2015
Nabarun Chakrabarty,1, ∗ Dilip Kumar Ghosh,2, †
Biswarup Mukhopadhyaya,1, ‡ and Ipsita Saha2, §
1
Regional Centre for Accelerator-based Particle Physics,
Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211019, India.
2
Department of Theoretical Physics,
Indian Association for the Cultivation of Science,
2A & 2B Raja S.C. Mullick Road, Kolkata 700 032, India
Abstract
We consider a two-Higgs doublet scenario containing three SU (2)L singlet heavy neutrinos with
Majorana masses. The second scalar doublet as well as the neutrinos are odd under a Z2 symmetry.
This scenario not only generates Majorana masses for the light neutrinos radiatively but also
makes the lighter of the neutral Z2 -odd scalars an eligible dark matter candidate, in addition to
triggering leptogenesis at the scale of the heavy neutrino masses. Taking two representative values
of this mass scale, we identify the allowed regions of the parameter space of the model, which are
consistent with all dark matter constraints. At the same time, the running of quartic couplings
in the scalar potential to high scales is studied, thus subjecting the regions consistent with dark
matter constraints to further requirements of vacuum stability, perturbativity and unitarity. It is
found that part of the parameter space is consistent with all of these requirements all the way up to
the Planck scale, and also yields the correct signal strength in the diphoton channel for the scalar
observed at the Large Hadron Collider.
∗
Electronic address:
Electronic address:
‡
Electronic address:
§
Electronic address:
†
[email protected]
[email protected]
[email protected]
[email protected]
1
IRFU-14-54
arXiv:1501.03699v1 [hep-ph] 15 Jan 2015
Modeling the pion
Generalized Parton Distribution
C. Mezrag1
IRFU/Service de Physique Nucl´eaire
CEA Saclay, F-91191 Gif-sur-Yvette, France
Abstract
We compute the pion Generalized Parton Distribution (GPD) in a
valence dressed quarks approach. We model the Mellin moments of
the GPD using Ans¨
atze for Green functions inspired by the numerical
solutions of the Dyson-Schwinger Equations (DSE) and the BetheSalpeter Equation (BSE). Then, the GPD is reconstructed from its
Mellin moment using the Double Distribution (DD) formalism. The
agreement with available experimental data is very good.
Keywords: GPD; pion; Dyson-Schwinger equations; Impulse approximation; Soft Pion Theorem
1
Introduction
Introduced in the 1990s [1, 2, 3], GPDs have been intensively studied both
theoretically and experimentally. Concerning the proton GPD, several models have emerged [4, 5, 6, 7, 8, 9] based on different kind of parametrizations,
and fitted to data. Here we focus on the pion GPD, which we model in
an original way through the triangle approximation, but using propagators
and vertices coming from the numerical solutions of the DSE and BSE. This
approach have been successful in the case of the pion Parton Distribution
Amplitude (PDA)[10]. In the first section, the details of the model will be
given. Mellin moment will be computed using functional forms coming from
the solutions of the DSE and BSE. The results will also be compared with
available experimental data. In the second sections, the main point will be
1
[email protected]
1
CCTP-2015-02
CCQCN-2015-60
Recent progress in backreacted
bottom-up holographic QCD
arXiv:1501.03693v1 [hep-ph] 15 Jan 2015
Matti Järvinen1
Laboratoire de Physique Théorique, École Normale Supérieure,
24 rue Lhomond, 75231 Paris Cedex 05, France
and
Crete Center for Theoretical Physics, Department of Physics,
University of Crete, 71003 Heraklion, Greece
Abstract. Recent progress in constructing holographic models for QCD is discussed, concentrating on the bottom-up models
which implement holographically the renormalization group flow of QCD. The dynamics of gluons can be modeled by using
a string-inspired model termed improved holographic QCD, and flavor can be added by introducing space filling branes in
this model. The flavor fully backreacts to the glue in the Veneziano limit, giving rise to a class of models which are called
V-QCD. The phase diagrams and spectra of V-QCD are in good agreement with results for QCD obtained by other methods.
Keywords: QCD, Holography, Veneziano limit, Conformal window
INTRODUCTION AND MOTIVATION
Holographic QCD has been the topic of numerous studies after the discovery of gauge/gravity duality. The studied models can be roughly divided into two classes, the
top-down and the bottom-up models.
The top-down models are fixed constructions directly
based on string theory and motivated by the original
AdS/CFT duality. In particular, the dual field theory can
usually be identified exactly, and the gravitational description does not bring in any extra parameters: all parameter of the gravitational action are uniquely fixed.
The ultimate goal of this kind of constructions would
be to to find an explicit holographic realization for the
infrared (IR) physics of QCD, at large number of colors Nc . However, so far the available models have some
shortcomings. Most importantly, when classical calculations are reliable on the gravity side, the low-energy
spectrum of the dual field theory has additional (KaluzaKlein) states at the same mass scale as the states of QCD.
Nevertheless, the observables computed in these models are in good agreement with our knowledge of QCD
(see [1, 2, 3] for concrete examples).
In the bottom-up approach one usually takes only the
main ideas from string theory. The holographic (often
five dimensional) model is constructed “by hand” by
picking the most important operators on the field theory side, and then writing down a natural action for
their dual fields. This means that the coupling constants,
masses and/or potentials of the constructed action are not
1
[email protected]
known, but need to be chosen by comparing the results to
the field theory. Therefore the holographic description is
necessarily effective and and a wide class of gauge theories is modeled instead of a definite single theory. Typically the action is chosen such that it respects general
symmetries and other features found in top-down constructions. They are able to produce a very precise description of QCD data (such as the meson spectrum) just
by fitting a few parameters. Well-known examples of this
type of models are [4, 5, 6]. Here we will discuss a specific bottom-up approach which is more strictly based on
string theory than is typical for bottom-up models.
So far the majority of the literature on holographic
QCD discusses flavor the ’t Hooft or probe limit, where
one takes Nc → ∞ keeping N f and the ’t Hooft coupling
g2YM Nc fixed. Here we will, however, also consider the
backreaction of the flavor to the glue, which is present if
we take the Veneziano limit instead. It is defined by
Nc → ∞ ,
Nf → ∞ ,
λ = g2YM Nc fixed ,
Nf
fixed .
x=
Nc
(1)
Backreaction means that the analysis will necessarily
be technically involved. Taking it into account is, however, important for several reasons. First, the number of
light quarks N f ∼ 2 . . . 3 is comparable to the number of
colors Nc = 3 for ordinary QCD, so that the backreaction
is expected to be strong. But there are also phenomena
(e.g., phase transitions) which cannot be accessed in the
probe limit at all. From arguments based on perturbation
theory, it is clear that QCD has the so called conformal
window: the theory has a nontrivial IR fixed point and
APCTP-Pre2015-001
Probing reheating with primordial spectrum
Jinn-Ouk Gonga,b ,
arXiv:1501.03604v1 [hep-ph] 15 Jan 2015
a Asia
Godfrey Leunga
and
Shi Pia
Pacific Center for Theoretical Physics, Pohang 790-784, Korea
of Physics, Postech, Pohang 790-784, Korea
b Department
Abstract
We study the impacts of reheating temperature on the inflationary predictions of the
spectral index and tensor-to-scalar ratio. Assuming that reheating process is very fast, the
reheating temperature can be constrained for sinusoidal oscillation within a factor of 10
- 100 or even better with the prospect of future observations. Beyond this, we find that
the predictions can also be insensitive to the reheating temperature in certain models,
including the Higgs inflation.
Electrical Conductivity of an Anisotropic Quark Gluon Plasma : A Quasiparticle
Approach
P. K. Srivastava∗, Lata Thakur† , and Binoy Krishna Patra‡
arXiv:1501.03576v1 [hep-ph] 15 Jan 2015
1
Department of Physics, Indian Institute of Technology Roorkee, Roorkee 247667, INDIA
The study of transport coefficients of strongly interacting matter got impetus after the discovery
of perfect fluid ever created at ultrarelativistic heavy ion collision experiments. In this article,
we have calculated one such coefficient viz. electrical conductivity of the quark gluon plasma
(QGP) phase which exhibits a momentum anisotropy. Relativistic Boltzmann’s kinetic equation
has been solved in the relaxation-time approximation to obtain the electrical conductivity. We
have used the quasiparticle description to define the basic properties of QGP. We have compared
our model results with the corresponding results obtained in different lattice as well as other model
calculations. Furthermore, we extend our model to calculate the electrical conductivity at finite
chemical potential.
PACS numbers: 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa
I.
INTRODUCTION
Transport coefficients are of particular interest to quantify the properties of strongly interacting matter created
at relativistic heavy ion collisions (HIC) and these
coefficients can be instrumental to study the critical
properties of QCD medium. The fluctuations or external
fields cause the system to depart from its equilibrium
and a non-equilibrium system has been created for a
brief time. The response of the system to such type of
fluctuations or external fields is essentially described by
transport coefficients eg. the shear and bulk viscosities,
the speed of sound etc. In recent years a somewhat
surprising result in the quark gluon plasma (QGP) story
has occurred when the practitioners in this field tried
to satisfy the collective flow data as obtained in collider
experiments. In order to get the required collective
flow in the framework of viscous hydrodynamics, the
value of shear viscosity to entropy density ratio (η/s)
comes out to be very small [1–3]. The tiny value of η/s
indicates the discovery of most perfect fluid ever created
in laboratory. This perfect fluid is described as strongly
interacting quark gluon plasma [4–7]. Thus the study
of various transport coefficients is a powerful tool to
really understand the behaviour of the matter produced
in the ultra relativistic heavy ion collision (uRHIC)
experiments at RHIC and LHC.
Recently electrical conductivity has gained a lot of
interest due to the strong electric field created in the
collision zone of uRHIC experiments [8–10]. It has been
observed that strong electric and magnetic fields are
created in peripheral heavy ion collisions whose strength
are roughly estimated as eE = eB = m2π (where mπ is
∗ [email protected]
† [email protected]
‡ binoyf [email protected]
the mass of the pion) within proper time 1 − 2 fm/c [11].
This large electrical field can significantly affect the
behaviour of the medium created in these collisions
and the effect depends on the magnitude of electrical
conductivity (σel ) of the medium. σel is responsible
for the production of electric current generated by
the quarks in the early stage of the collision. The
value of σel would be of fundamental importance for
the strength of Chiral Magnetic Effect [12] which is a
signature of CP-violation in strong interaction. Further
the electrical field in mass asymmetric collisions (e.g.
Cu-Au collisions etc.) has overall a preferred direction
and thus generating a charge asymmetric flow whose
strength is directly related to σel [13]. Furthermore, σel
is related with the emission rate of soft photons [14]
accounting for their raising spectra [15, 16]. Despite of
the importance of electrical conductivity, it has been
studied rarely in the literature for the QGP phase.
With the discovery of “most perfect fluid ever generated”, another important observation has been made
that this fluid possesses momentum-space anisotropies in
the local rest frame (LRF) [17, 18]. This has important
implications for both dynamics and signatures of the
QGP. Earlier it has been assumed a priori in the ideal
hydrodynamics that the QGP is completely isotropic.
However, recently dissipative hydrodynamics helps us
to understand that the QGP created in ultrarelativistic
heavy ion collisions has different longitudinal and
transverse pressure. It has been shown heuristically in
first-order Navier Stokes viscous hydrodynamics that
the ratio of longitudinal pressure over the transverse
pressure is: PL /PT = (3τ T − 16¯
η )/(3τ T + 8¯
η ), where
η¯ = η/s [17]. Using the RHIC-like initial condition the
value of PL /PT comes out equal to 0.5 and for LHC-like
initial condition this ratio takes the value as 0.35 [17].
It has also been shown that there exists an anisotropy
in PL versus PT in second-order Israel-Stewart viscous hydrodynamics. Several other groups who study
the early-time dynamics of QCD within AdS/CFT
CNU-HEP-15-01
Higgcision in the Minimal Supersymmetric Standard Model
Kingman Cheung1,2 , Jae Sik Lee3 , and Po-Yan Tseng1
1
Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan
arXiv:1501.03552v1 [hep-ph] 15 Jan 2015
2
Division of Quantum Phases and Devices, School of Physics,
Konkuk University, Seoul 143-701, Republic of Korea
3
Department of Physics, Chonnam National University,
300 Yongbong-dong, Buk-gu, Gwangju, 500-757, Republic of Korea
(Dated: January 16, 2015)
Abstract
We perform global fits to the most recent data (after summer 2014) on Higgs boson signal
strengths in the framework of the minimal supersymmetric standard model (MSSM). The heavy
supersymmetric (SUSY) particles such as squarks enter into the loop factors of the Hgg and Hγγ
vertices while other SUSY particles such as sleptons and charginos also enter into that of the Hγγ
vertex. We also take into account the possibility of other light particles such as other Higgs bosons
and neutralinos, such that the 125.5 GeV Higgs boson can decay into. We use the data from
the ATLAS, CMS, and the Tevatron, with existing limits on SUSY particles, to constrain on the
relevant SUSY parameters. We obtain allowed regions in the SUSY parameter space of squark,
slepton and chargino masses, and the µ parameter.
1
arXiv:1501.03520v1 [hep-ph] 14 Jan 2015
January 15, 2015
Natural Inflation from 5D SUGRA
and Low Reheat Temperature
Filipe Paccetti Correia a1 , Michael G. Schmidt b2 , and Zurab Tavartkiladze c3
a
Deloitte Consultores, S.A., Pra¸ca Duque de Saldanha, 1 - 6 o, 1050-094 Lisboa, Portugal 4
b
Institut f¨
ur Theoretische Physik, Universit¨at Heidelberg, Philosophenweg 16,
69120 Heidelberg, Germany
c
Center for Elementary Particle Physics, ITP, Ilia State University, 0162 Tbilisi, Georgia
Abstract
Motivated by BICEP2’s recent observation of a possibly large primordial tensor component
r of inflationary perturbations, we reanalyse in detail the 5D conformal SUGRA originated
natural inflation model of Ref. [1]. The model is a supersymmetric variant of 5D extra natural
inflation, also based on a shift symmetry, and leads to the potential of natural inflation.
Analysis of the required number of e-foldings (from the CMB observations) points to the
necessity of a very weak inflaton decay and low reheating temperature Tr . We show that this
< O(100) GeV. This is realized
can be naturally achieved within 5D gauge inflation giving Tr ∼
by coupling the bulk fields, generating the inflaton potential, with brane SM states. Some
related theoretical issues of the construction, along with phenomenological and cosmological
implications, are also discussed.
1
E-mail: [email protected]
E-mail: [email protected]
3
E-mail: [email protected]
4
Disclaimer: This address is used by F.P.C. only for the purpose of indicating his professional affiliation. The
contents of the paper are limited to Physics and in no ways represent views of Deloitte Consultores, S.A.
2
1
Galactic Center Excess in Gamma Rays from Annihilation of Self-Interacting Dark
Matter
Manoj Kaplinghat
Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
Tim Linden
Kavli Institute for Cosmological Physics, University of Chicago, IL 60637, USA
Hai-Bo Yu
The Galactic Center excess. Recent Fermi-LAT observations of the Galactic Center (GC) of the Milky Way
have uncovered a stunning γ-ray excess compared to
expectations from diffuse astrophysical emission [1–11].
While these studies differ in the astrophysical background
models, they all agree on three key features of the γ-ray
excess: (1) the spectrum is strongly peaked at an energy
of approximately 2 GeV, with a low-energy spectrum that
is harder than expected from π 0 -emission, (2) the excess
radially extends to at least 10◦ from the GC, following
an emission profile that falls with distance (r) from the
GC as r−α with α = 2.0 – 2.8, and (3) the excess is
roughly spherically symmetric, without any evidence of
elongation parallel or perpendicular to the galactic plane.
While other explanations have been discussed [4, 5, 12–
15], dark matter remains a compelling possibility. The
detection of an excess with the same spectrum toward
dwarf spheroidal galaxies surrounding the Milky Way
would verify this possibility. However, no equivalent signal has been observed in dwarf spheroidal galaxies [16],
which stands in mild tension with some models of the
GC excess [17].
In fact, dwarf galaxies have long challenged our understanding of the nature of dark matter. The dark matter
halos of dwarf galaxies have constant density cores [18–
21], in contrast to the cuspy profile predicted by simulations of cold collisionless dark matter (CDM). Additionally, CDM predicts a population of dwarf halos that are
systematically denser than the dwarf spheroidal galaxies in the Milky Way [22], Andromeda [23], or Local
Group [24, 25]. A compelling solution to these challenges is to assume that dark matter strongly interacts
with itself [26, 27]. Recent simulations have shown that
nuclear-scale dark matter self-interaction cross sections
can produce heat transfer from the hot outer region to
the cold inner region of dark matter halos, reducing the
central densities of dwarf galaxies in accordance with observations [28–31].
Connection to dark matter self-interactions. We
explore the intriguing possibility that the GC γ−ray excess is caused by Inverse Compton (IC) scattering of energetic e+ e− from dark matter annihilation, and the absence of the GeV γ-ray signal in dwarf spheroids is a natural consequence of self-interacting dark matter (SIDM)
models. Our key observations are as follows:
• Energetic e+ e− from dark matter annihilation (or
another extended source distribution) can effectively produce γ-rays in the GC through IC and
bremsstrahlung, due to the high interstellar radiation field (ISRF) and gas densities in this region.
The IC emission can explain the peak of the GC
signal (at 2-3 GeV) for dark matter masses in the
approximate mass range of 20-60 GeV. The crucial
requirement is the presence of a new source of e+ e−
with energies larger than 20 GeV, which produce
γ-rays with peak energy of ∼ (20 GeV/me )2 EISRF ,
with typical ISRF photon energy EISRF ∼ 1 eV.
• The AMS-02 constraint [32] demands a softer electron spectrum than direct annihilation to e+ e− and
hence annihilation through a light mediator is a
natural solution1 .
1
Another possibility, which we do not explore here, is direct annihilation to µ+ µ− , with e and τ channels suppressed.
2
• A nuclear-scale dark matter self-scattering cross
section requires a dark force carrier with a mass below ∼ 100 MeV [33–35]. Annihilations through this
mediator can kinematically couple only to e+ e−
and neutrinos in the standard model sector.
• The e+ e− produced via dark matter annihilation do
not produce appreciable γ-rays from dwarf galaxies
due to their low starlight and gas densities. The
dominant signal in these systems should be due to
final state radiation, with a cross section suppressed
by αEM .
• The SIDM density profile in the central region of
the Milky Way is determined by the bulge potential [36]. Models of the galactic bulge imply that
the dark matter density increases to within 1-2◦
from the GC and the annihilation power is significantly enhanced compared to the predictions of
SIDM-only simulations.
A hidden sector dark matter model. We consider
a simple hidden sector model in which a 50 GeV dark
matter particle couples to a vector mediator φ. The
relic density in this model is set by the annihilation
process χχ
¯ → φφ with an annihilation cross section
4.4ξ × 10−26 cm3 s−1 for a Dirac particle [37], where ξ
is the ratio of the temperature of the hidden sector to
that of the visible sector at freeze-out [38]. We assume
that the hidden and visible sectors are coupled through
kinetic [39] or Z-mixing [40] leading to φ → e+ e− decays [41]. The dark matter mass utilized here illustrates
our main points; the mass could be large or smaller by
about 50%, depending on the details of electron energy
loss in the GC.
In order to compute the secondary emission from this
model we utilize the software PPPC4DMID [42], which provides the solution for one-dimensional diffusion with spatially dependent energy losses. We use the “MED” diffusion parameters listed in PPPC4DMID [42]. This software calculates the γ-ray spectrum from IC scattering assuming an interstellar radiation field energy density from
GALPROP [43], an exponential magnetic field profile [44],
and negligible bremsstrahlung losses, which is a good approximation for the & 10 GeV electrons under consideration. We tested the PPPC4DMID spectrum by writing an
independent code that solves the one-dimensional diffusion equation assuming spatially-constant energy losses
and found good agreement.
In Fig. 3, we compare the intensity and spectrum
from our model to the region of interest (ROI) 1 of
Ref. [10], which includes regions within 5◦ radius (about
750 pc projected distance at the GC) excluding latitudes
|b| < 2◦ , finding good agreement.
These results show that the secondary IC emission effectively reproduces the hard spectral bump at an energy
of ∼2 GeV, and the relatively hard spectrum component
at energies above 10 GeV observed by Ref. [10]. The
hard spectrum component is an important discriminator
Inverse Compton+FSR
E2 dNdE H10-6 GeV2 cm2 ssrGeVL
arXiv:1501.03507v1 [hep-ph] 14 Jan 2015
Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
Observations by the Fermi-LAT telescope have uncovered a significant γ-ray excess toward the
Milky Way Galactic Center. There has been no detection of a similar signal in the direction of the
Milky Way dwarf spheroidal galaxies. Additionally, astronomical observations indicate that dwarf
galaxies and other faint galaxies are less dense than predicted by the simplest cold dark matter
models. We show that a self-interacting dark matter model with a particle mass of roughly 50 GeV
annihilating to the mediator responsible for the strong self-interaction can simultaneously explain all
three observations. The mediator is necessarily unstable and its mass must be below about 100 MeV
in order to lower densities in faint galaxies. If the mediator decays to electron-positron pairs with
a cross section on the order of the thermal relic value, then we find that these pairs can up-scatter
the interstellar radiation field and produce the observed γ-ray excess. We show that this model is
compatible with all current constraints and highlight detectable signatures unique to self-interacting
dark matter models.
8
FSR HpromptL
æ
æ
æ
6
æ
æ
æ
2
æ
æ
æ
æ
æ
æ
æ
æ
æ
4
æ
æ
æ
æ
æ
æ
æ
0
0.3
æ
0.5
1
3
5
10
E HGeVL
30
50
FIG. 1. γ-ray spectrum from Inverse Compton emission and
final state radiation produced by annihilation of a 50 GeV
dark matter particle through a light mediator into e+ e− final state. The spectrum is compared to the Galactic Center
excess [10].
of the dark matter mass, as it absent for masses closer to
20 GeV.
We estimate the range of cross sections required to produce this signal as 0.3−2×10−26 cm3 /s, corresponding to
the SIDM density profiles shown in Fig. 2 and discussed
next. In order to estimate this cross section range we
noted (using the density profiles available in PPPC4DMID)
that the IC signal R(shown in Fig. 3) is proportional to
the J-factor (J = d`ρ2 (`, Ω), where ` = line of sight)
within 5 degrees of the GC at the 10% accuracy level.
Therefore, we scale the PPPC4DMID result using the Jfactors for the SIDM density profiles to obtain the cross
section range.
Density profile of SIDM. The cross section estimate
depends on the dark matter density profile. The expectation from SIDM-only simulations is that the SIDM density profile would be essentially constant in this region.
However, when baryons dominate, as expected in the inner galaxy, it has been shown that the equilibrium SIDM
density profile tracks the baryonic potential [36]. We
compute the equilibrium SIDM density profile assuming
two possibilities for the early (before self-interactions become effective) dark matter density profile following the
method in Ref. [36]: an NFW profile [45] with scale factor rs = 26 kpc [46] and the same profile after adiabatic
contraction [47] due to the disk and bulge of the Milky
Way. The early profiles set the boundary conditions for
the equilibrium solutions.
We determine the consistency of this scenario by fitting to the composite galactic rotation curve of Ref. [48]
shown in the top panel of Fig. 2 including a black hole
of mass 4 × 106 M , inner and outer spherical bulges
with exponential density profiles, an exponential disk
and a spherical halo. The SIDM halo is computed selfconsistently from the spherically-averaged stellar distri-
A 3.55 keV Line from Exciting Dark Matter without a Hidden Sector
Asher Berlin,1, 2 Anthony DiFranzo,3, 4 and Dan Hooper3, 5
1
Enrico Fermi Institute, University of Chicago, Chicago, IL 60637
Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637
3
Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, IL 60510
4
Department of Physics and Astronomy, University of California, Irvine, CA 92697
5
Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637
arXiv:1501.03496v1 [hep-ph] 14 Jan 2015
2
Models in which dark matter particles can scatter into a slightly heavier state which promptly
decays to the lighter state and a photon (known as eXciting Dark Matter, or XDM) have been shown
to be capable of generating the 3.55 keV line observed from galaxy clusters, while suppressing the flux
of such a line from smaller halos, including dwarf galaxies. In most of the XDM models discussed in
the literature, this up-scattering is mediated by a new light particle, and dark matter annihilations
proceed into pairs of this same light state. In these models, the dark matter and mediator effectively
reside within a hidden sector, without sizable couplings to the Standard Model. In this paper, we
explore a model of XDM that does not include a hidden sector. Instead, the dark matter both
up-scatters and annihilates through the near resonant exchange of a O(102 ) GeV pseudoscalar with
large Yukawa couplings to the dark matter and smaller, but non-neglibile, couplings to Standard
Model fermions. The dark matter and the mediator are each mixtures of Standard Model singlets
and SU (2)W doublets. We identify parameter space in which this model can simultaneously generate
the 3.55 keV line and the gamma-ray excess observed from the Galactic Center, without conflicting
with constraints from colliders, direct detection experiments, or observations of dwarf galaxies.
PACS numbers: 95.35.+d, 95.85.Pw; FERMILAB-PUB-15-009-A
I.
INTRODUCTION
The nature of dark matter remains one of the most
elusive and longstanding problems in physics today. As
a consequence, much attention has been given to observational anomalies that can be plausibly interpreted in
terms of dark matter interactions. One such signal is
an approximately 3.55 keV X-ray line that has been observed from a number of galaxy clusters, as well as from
the nearby Andromeda Galaxy.
The first reported evidence for the 3.55 keV line was
found in data from the XMM-Newton satellite, from the
directions of a stacked sample of 73 low redshift galaxy
clusters [1]. Shortly thereafter, a similar line was reported from the directions of the Perseus Cluster and the
Andromeda Galaxy [2]. A study of XMM-Newton data
also suggests the existence of a 3.55 keV line from the direction of the Milky Way’s center [3] (see also, however,
Ref [4]). More recently, the line was identified within
Suzaku data from the Perseus Cluster [5].
A number of interpretations for these observations
have been proposed. On the one hand, it has been suggested that atomic transitions (such as those associated
with the chlorine or potassium ions, Cl-XVII and KXVIII, for example [6]) might be responsible for the line,
although the viability of this explanation is currently unclear [7–9]. Alternatively, decaying dark matter particles
could generate such an X-ray line. Particularly well motivated is dark matter in the form of an approximately
7 keV sterile neutrino, which decays through a loop to
a photon and an active neutrino. If one assumes that
all of the dark matter consists of 7 keV sterile neutrinos, the observed X-ray line flux implies a mixing angle
of sin2 (2θ) ∼ 7 × 10−11 . With such a small degree of
mixing, however, the standard Dodelson-Widrow mechanism of production via the collision-dominated oscillation
conversion of thermal active neutrinos [10] leads to an
abundance of sterile neutrinos that corresponds to only a
few percent of the total dark matter density, thus requiring additional resonant or otherwise enhanced production
mechanisms. Alternatively, sterile neutrinos with a larger
mixing angle of sin2 (2θ) ∼ 3 × 10−10 could naturally constitute roughly 10% of the dark matter abundance, and
decay at a rate that is sufficient to generate the observed
line flux.
Interpretations of the X-ray line in terms of decaying
dark matter are in considerable tension, however, with
studies of galaxies using Chandra and XMM-Newton
data [11] and dwarf spheroidal galaxies using XMMNewton data [12], which do not detect a line at the
level predicted by decaying dark matter scenarios. One
way to potentially reconcile the intensity of the line observed from clusters with the null results from dwarfs and
other smaller systems is to consider the class of scenarios
known as eXciting Dark Matter (XDM) [13–16]. In such
models, the collisions of dark matter particles can cause
them to up-scatter into an excited state, χ1 χ1 → χ2 χ2 or
χ1 χ1 → χ1 χ2 . For a mass splitting of mχ2 − mχ1 ' 3.55
keV, the subsequent decays of the slightly heavier state
can generate a 3.55 keV photon, χ2 → χ1 γ. Critical
to the problem at hand are the kinematics of the XDM
scenario, which introduce a velocity threshold for upscattering, suppressing the X-ray flux from dwarf galaxies (and, to a lesser extent, from larger galaxies)[15, 17].
Within the paradigm of XDM, the observations of clusters, galaxies, and dwarf galaxies can be mutually con-
Interpreting the CMS `+ `− jjE
/T Excess with a Leptoquark Model
Ben Allanacha , Alexandre Alvesb ,∗ Farinaldo S. Queirozc,d,e , Kuver Sinhaf , and Alessandro Strumiag,h
a
DAMTP, CMS, Wilberforce Road, University of Cambridge, Cambridge, CB3 0WA, United Kingdom
Departamento de Ciˆencias Exatas e da Terra, Universidade Federal de S˜ao Paulo, Diadema-SP, 09972-270, Brasil
c
Department of Physics and Santa Cruz Institute for Particle Physics University of California, Santa Cruz, CA 95064, USA
d
Max-Planck-Institut f¨ur Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
e
International Institute of Physics, UFRN, Av. Odilon Gomes de Lima, 1722 - Capim Macio - 59078-400 - Natal-RN,
Brazil f Department of Physics, Syracuse University, Syracuse, NY 13244, USA
g
Dipartimento di Fisica dell’ Universita di Pisa and INFN, Italy
h
National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
(Dated: January 16, 2015)
Motivated by excesses in eejj and eνjj channels observed by the CMS collaboration, in 8 TeV LHC data,
a model of lepto-quarks with mass around 500 GeV was proposed in the literature. In order to reproduce the
claimed event rate, lepto-quarks were assumed to have a significant partial branching ratio into an extra sector,
taken to be Dark Matter, other than the canonical ej. We here show that the decay channel of lepto-quark into
Dark Matter can fit another excess claimed by CMS, in `+ `− jjE
/T : the event rate, the distribution in di-lepton
invariant mass and the rapidity range are compatible with the data. We provide predictions for the forthcoming
Run II of the 14 TeV LHC and discuss aspects of dark matter detection.
200
INTRODUCTION
The CMS collaboration reported a 2.6σ excess compared
with Standard Model expectations in `+ `− jjE
/T events, containing two opposite-sign same-flavor leptons ` = {e, µ}, at
least two jets and missing transverse momentum E
/T [1]. No
similar ATLAS analysis has been presented. The CMS analysis was performed with 19.4 fb−1 of integrated luminosity at
a center of mass energy of 8 TeV. The excess was found in
the central region with lepton pseudo-rapidities |η` | ≤ 1.4,
after various event selection and flavor subtraction cuts, and
in the kinematical region with di-lepton invariant mass m`` <
80 GeV, as shown in Fig. 1. No excess is seen in other regions
nor in the trilepton channel.
The excess was found in the context of CMS searches for
edges in m`` . The triangular edge is a classic supersymmetry
signal, and interpretations of the CMS excess in the context
of the so-called golden cascade (χ
˜02 → `˜± `∓ → χ
˜01 `± `∓ )
0
0
˜
have been proposed (χ
˜1 , χ
˜2 , and ` are the lightest neutralino,
the next-to-lightest neutralino and the slepton, respectively).
Since direct electroweak production of χ
˜02 has too small a
cross section to provide a large enough rate whilst evading
previous collider bounds from LEP, assistance from colored
particle production is required. The decay chain could start
with t˜ → tχ
˜02 [2] or q˜ → q χ
˜02 [3]. The former interpretation is
constrained by the fact that the CMS study did not observe a
large excess in trilepton final states, which should be present
from the leptonic top quark decay. The latter case will be
increasingly constrained as the exclusion limits on first two
generation squarks becomes stronger. The CMS study itself
opted for an explanation in terms of light sbottoms ˜b → bχ
˜02 ,
and χ
˜02 → χ
˜01 `+ `− , although no b-jet requirement was made
on the final states. Ref. [4] explored the parameter space in
order to simultaneously satisfy bounds from 4 charged lepton production. The purpose of the present letter is to show
that the CMS excess can be explained by a different, non-
Events  5GeV
arXiv:1501.03494v1 [hep-ph] 14 Jan 2015
b
Data
150
S+B
FS
100
DY
SignalHCL
50
0
50
100
150
Mll @GeVD
200
250
300
FIG. 1. Di-lepton invariant mass spectrum of CMS `+ `− jjE
/T
events: expected non-DY background (black histogram), expected
DY (red histogram), expected signal for benchmark C (green histogram) and expected signal plus background for benchmark C (blue
histogram).19 signal events are expected for m`` > 100 GeV, which
is compatible with CMS data.
supersymmetric, class of models that were introduced for a
different purpose. A CMS search [5, 6] for leptoquarks (LQs)
[7] - [13] found a mild excess in the eejj and eνjj channels,
giving hints for a first-generation scalar lepto-quark with mass
500−650 GeV and branching ratio of the lepto-quark into leptons and quarks of ≈ 15% [5]. In the model presented in [14]
a Dark Matter sector was added to account for the missing
branching ratio. This extra decay channel of the LQ enables
us to fit the CMS `+ `− jjE
/T excess.
/T excess can be reproFig. 1 exemplifies how the `+ `− jjE
duced by lepto-quarks with ≈ 500 GeV masses: the model
predicts a peak in m`` , which fits data roughly as well as the
triangular edge searched for by CMS. The model also predicts
small numbers of events in the forward region and for trilepton final states, also compatible with the CMS measurements.
Coulomb breakup of 37Mg and its ground state structure
Shubhchintak, Neelam, R. Chatterjee
arXiv:1501.03642v1 [nucl-th] 15 Jan 2015
Department of Physics, Indian Institute of Technology - Roorkee, 247667, India
R. Shyam
Theory Group, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064,
India, and Department of Physics, Indian Institute of Technology, Roorkee-247667, India
K. Tsushima
International Institute of Physics, Federal University of Rio Grande do Norte Av. Odilon
Gomes de Lima, 1722 Capim Macio, Natal, RN 59078-400, Brazil
Abstract
We calculate Coulomb breakup of the neutron rich nucleus 37 Mg on a Pb
target at the beam energy of 244 MeV/nucleon within the framework of a
finite range distorted wave Born approximation theory that is extended to
include the effects of projectile deformation. In this theory, the breakup
amplitude involves the full wave function of the projectile ground state.
Calculations have been carried out for the total one-neutron removal cross
section (σ−1n ), the neutron-core relative energy spectrum, the parallel momentum distribution of the core fragment, the valence neutron angular, and
energy-angular distributions. The calculated σ−1n has been compared with
the recently measured data to put constraints on the spin parity, and the oneneutron separation energy (S−1n ) of the 37 Mg ground state (37 Mggs ). The
dependence of σ−1n on the deformation of this state has also been investigated. Our study suggests that 37 Mggs is most likely to have a spin parity
assignment of 3/2− . Using the shell model value for the spectroscopic factor for this configuration and without considering the projectile deformation
effects, a S−1n of 0.10 ± 0.02 MeV is extracted. Inclusion of the deformaEmail addresses: [email protected] (Shubhchintak), [email protected]
(Neelam), [email protected] (R. Chatterjee), [email protected] (R.
Shyam), [email protected] (K. Tsushima)
Preprint submitted to Elsevier
January 16, 2015
arXiv:1501.03797v1 [nucl-ex] 15 Jan 2015
Resonances as Probes of Heavy-Ion Collisions at
ALICE
A. G. Knospe (for the ALICE Collaboration)
The University of Texas at Austin, Department of Physics, Austin, TX, USA
E-mail: [email protected]
Abstract. Hadronic resonances serve as unique probes in the study of the hot and dense
nuclear matter produced in heavy-ion collisions. Properties of the hadronic phase of the collision
can be extracted from measurements of the suppression of resonance yields. A comparison of the
transverse-momentum spectra of the φ(1020) meson and the proton (which have similar masses)
can be used to study particle production mechanisms. Resonance measurements in pp collisions
provide input for tuning QCD-inspired particle production models and serve as reference
measurements for other collision systems. Measurements of resonances in p–Pb collisions
allow nuclear effects in the absence of a hot and dense final state to be studied. The ALICE
Collaboration has measured resonances in pp, p–Pb, and Pb–Pb collisions. These measurements
will be discussed and compared to results from other experiments and to theoretical models.
Resonances serve as useful probes that allow the characteristics of heavy-ion collisions to be
studied at different stages of their evolution. While the yields of stable hadrons are fixed at
chemical freeze-out, the yields of resonances can be modified by hadronic scattering processes
after chemical freeze-out [1–3]. Regeneration, in which resonance decay products scatter pseudoelastically through a resonance state (e.g., πK → K∗0 → πK), can increase the measured yield
of the intermediate resonance state without changing the yields of the stable hadrons. Elastic
re-scattering of a resonance decay product can smear the invariant mass resolution and may
impede reconstruction of the original resonance. Pseudo-elastic scattering of a resonance decay
product through a different resonance state (e.g., a pion from a K∗0 decay scattering through
a ρ state) will prevent reconstruction of the first resonance [4]. Regeneration and re-scattering
are expected to be most important for pT . 2 GeV/c [1, 4]. The final resonance yields at
kinetic freeze-out will be determined by the chemical freeze-out temperature, the time between
chemical and kinetic freeze-out, the resonance lifetime, and the scattering cross sections of its
decay products with other hadrons. Theoretical models that take these effects into account can
be used to estimate the properties of the hadronic phase using measured resonance yields (or
their ratios to stable particles) as input [2, 5, 6].
In addition, partial restoration of chiral symmetry around the phase transition between
partonic and hadronic matter may lead to changes in the masses or the widths of resonances [7–
10]. Mechanisms that determine the shapes of particle pT spectra, including the relative
strengths of quark recombination [11, 12] and hydrodynamical effects [13–15], are studied
experimentally using many different particle species; the φ(1020), a meson with a mass similar to
the proton, provides valuable information regarding the effects of mass and baryon number on the
shapes of particle pT spectra. Measurements of the nuclear modification factor RAA of hadrons
allows the in-medium energy loss of partons to be studied. Resonance RAA measurements will
arXiv:1501.03773v1 [nucl-ex] 15 Jan 2015
A Monte Carlo Study of Multiplicity Fluctuations
in Pb-Pb Collisions at LHC Energies
Ramni Gupta∗
Department of Physics & Electronics, University of Jammu, Jammu, India
January 16, 2015
Abstract
With large volumes of data available from LHC, it has become possible
to study the multiplicity distributions for the various possible behaviours of
the multiparticle production in collisions of relativistic heavy ion collisions,
where a system of dense and hot partons has been created. In this context
it is important and interesting as well to check how well the Monte Carlo
generators can describe the properties or the behaviour of multiparticle production processes. One such possible behaviour is the self-similarity in the
particle production, which can be studied with the intermittency studies and
further with chaoticity/erraticity, in the heavy ion collisions. We analyse the
behaviour of erraticity index in central Pb-Pb collisions at centre of mass
energy of 2.76 TeV per nucleon using the AMPT monte carlo event generator, following the recent proposal by R.C. Hwa and C.B. Yang, concerning
the local multiplicity fluctuation study as a signature of critical hadronization
in heavy-ion collisions. We report the values of erraticity index for the two
versions of the model with default settings and their dependence on the size
of the phase space region. Results presented here may serve as a reference
sample for the experimental data from heavy ion collisions at these energies.
∗ email:[email protected]
1
Submitted to ’Chinese Physics C’
High-spin level structure of the neutron-rich nucleus
91
Y
Xiao-Feng HE1,2;1 , Xiao-Hong ZHOU1;2 , Yong-De Fang1 , Min-Liang Liu1 , Yu-Hu ZHANG1 , Kai-Long WANG1,2 ,
Jian-Guo WANG1 , Song GUO1 , Yun-Hua QIANG1 , Yong ZHENG1 , Ning-Tao ZHANG1 , Guang-Shun LI1 ,
Bing-Shui GAO1,2 , Xiao-Guang WU3 , Chuang-Ye HE3 , Yun ZHENG3
arXiv:1501.03596v1 [nucl-ex] 15 Jan 2015
1
Key Laboratory of High Precision Nuclear Spectroscopy and Center for Nuclear Matter Science, Institute of Modern Physics,
Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China
2 University of Chinese Academy of Sciences, Beijing 000049, People’s Republic of China
3 China Institute of Atomic Energy, Beijing 102413, People’s Republic of China
Abstract: High-spin level structure of the neutron-rich nucleus 91 Y has been reinvestigated via the 82 Se(13 C,
p3n)91 Y reaction. A newly constructed level scheme including several key levels clarifies the uncertainties in the
earlier studies. These levels are characterized by the breaking of the Z = 38 and N = 56 subshell closures, which
involves in the spin-isospin dependent central force and tensor force.
Key words: neutron-rich nucleus, level scheme, spin-isospin dependent central force, tensor force
PACS: 21.10.Re, 23.20.-g, 23.20.Lv, 27.70.+q
1
Introduction
lematic via the conventional (HI, xn) reaction. Highspin states of 91 Y have been initially investigated via
fusion-evaporation reaction 82 Se(12 C, p2n)91 Y [9]. It was
not until recently that an extended level scheme is constructed by means of the fission of 221 Pa produced by
a 24 Mg beam impinging on a 173 Yb target [10]. In this
work, the high-spin level structure is reinvestigated and
the configurations are figured out, in analogy to our earlier study of the N = 52 isotone 92 Zr [11].
It is well known that the high-spin states of nearspherical nuclei can be constructed by the aligned angular momentum of open shell nucleons. The maximum
spin occurs at the configuration termination in the valence space. To generate higher-spin states, the shell closure should be broken. A number of studies have revealed
such excitation process for nuclei around the quasidoubly
magic nucleus 88 Sr [1–4].
The low-lying levels of nuclei with 38 < Z < 50 and
50 < N < 56 are dominated by the valence-nucleon excitations within the π(p1/2 , g9/2 ) and νd5/2 shell-model
orbitals. The medium- or high-spin levels can be understood as the particle-hole excitations. Federman et
al. have theoretically studied the proton p3/2 → p1/2
and neutron d5/2 → g7/2 excitations [5, 6] and given the
reasonable explanations for the reductions of the Z = 38
and N = 56 energy gaps. The proton-neutron interaction
includes tensor force and the spin-isospin dependent central force [7, 8]. In the picture of tensor force [7], the enhanced πp1/2 −νd5/2 and reduced πp3/2 −νd5/2 monopole
interaction may arise from the tensor component if the
others contribute the same interactional values. Hence,
when the νd5/2 orbital is occupied by more neutrons, the
πp1/2 orbital goes down while πp3/2 orbital comes up,
that is, the Z = 38 energy gap becomes smaller. Likewise, the reduction of the N = 56 gap can be associated
with the spin-orbital partners πg9/2 and νg7/2 [6], between which the interaction is the so-called spin-isospin
dependent central force [8].
The production of neutron-rich nucleus 91 Y is prob-
2
Experiment
High-spin states of 91 Y were populated through the
Se(13 C, p3n)91 Y reaction. The 13 C beam was provided
by the HI-13 Tandem Accelerator of the China Institute of Atomic Energy(CIAE), and the target was 2.11
mg/cm2 isotopically enriched 82 Se on 8.56 mg/cm2 natural lead backing. The emitted γ rays from the reaction products were detected by an array consisting of
2 planar and 12 Compton-suppressed HPGe detectors.
The energy and efficiency calibrations were made using the 60 Co, 133 Ba, and 152 Eu standard sources and the
typical energy resolution was 2.0∼2.5 keV at full width
at half-maximum (FWHM) for the 1332.5-keV γ ray of
60
Co. Events were collected when at least 2 detectors are
fired within the prompt 80 ns coincidence time window.
Under these conditions, a total of 2.5×107 coincidence
events were recorded and the data was sorted into a symmetrized Eγ −Eγ matrix for subsequent off-line analysis.
In order to obtain multipolarity information of the
emitted γ rays, two asymmetric coincidence matrices
were constructed using the γ rays detected at all angles
82
1) E-mail: [email protected]
2) E-mail: [email protected]
1