2,080 research outputs found
Perspective of monochromatic gamma-ray line detection with the High Energy cosmic-Radiation Detection (HERD) facility onboard China's Space Station
HERD is the High Energy cosmic-Radiation Detection instrument proposed to
operate onboard China's space station in the 2020s. It is designed to detect
energetic cosmic ray nuclei, leptons and photons with a high energy resolution
( for electrons and photons and for nuclei) and a large
geometry factor ( for electrons and diffuse photons and for nuclei). In this work we discuss the capability of HERD to detect
monochromatic -ray lines, based on simulations of the detector
performance. It is shown that HERD will be one of the most sensitive
instruments for monochromatic -ray searches at energies between
to a few hundred GeV. Above hundreds of GeV, Cherenkov telescopes will
be more sensitive due to their large effective area. As a specific example, we
show that a good portion of the parameter space of a supersymmetric dark matter
model can be probed with HERD.Comment: 9 pages, 7 figures, matches version published in Astropart.Phy
Global Study of the Simplest Scalar Phantom Dark Matter Model
We present a global study of the simplest scalar phantom dark matter model.
The best fit parameters of the model are determined by simultaneously imposing
(i) relic density constraint from WMAP, (ii) 225 live days data from direct
experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT
indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the
Higgs boson candidate with a mass about 125 GeV and its invisible branching
ratio no larger than 40% if the decay of the Higgs boson into a pair of dark
matter is kinematically allowed. The allowed parameter space is then used to
predict annihilation cross sections for gamma-ray lines, event rates for three
processes mono-b jet, single charged lepton and two charged leptons plus
missing energies at the Large Hadron Collider, as well as to evaluate the muon
anomalous magnetic dipole moment for the model.Comment: Matches JCAP accepted version. 25 pages, 7 figure
T2 Values of Posterior Horns of Knee Menisci in Asymptomatic Subjects
[[abstract]]Purpose: The magnetic resonance (MR) T2 value of cartilage is a reliable indicator of tissue properties and therefore may be used as an objective diagnostic tool in early meniscal degeneration. The purpose of this study was to investigate age, gender, location, and zonal differences in MR T2 value of the posterior horns of knee menisci in asymptomatic subjects. Methods: Sixty asymptomatic volunteers (30 men and 30 women) were enrolled and divided into three different age groups: 20–34, 35–49 and 50–70 years. The inclusion criteria were BMI<30 kg/cm2, normalized Western Ontario and McMaster Universities (WOMAC) pain score of zero, and no evidence of meniscal and ligamentous abnormalities on routine knee MR imaging. The T2 values were measured on images acquired with a T2-weighted fat-suppressed turbo spin-echo sequence at 3T. Results: The mean T2 values in both medial and lateral menisci for the 20–34, 35–49, and 50–70 age groups were 9.94 msec±0.94, 10.73 msec±1.55, and 12.36 msec±2.27, respectively, for women and 9.17 msec±0.74, 9.64 msec±0.67, and 10.95 msec±1.33, respectively, for men. The T2 values were significantly higher in the 50–70 age group than the 20–34 age group (P<0.001) and in women than in men (P = 0.001, 0.004, and 0.049 for each respective age group). T2 values were significantly higher in medial menisci than in lateral menisci only in women age 50–70 (3.33 msec, P = 0.006) and in the white zone and red/white zone of the 50–70 and 35–49 age groups than that of the 20–34 age group (2.47, 1.02; 2.77, 1.16 msec, respectively, all P<0.01). Conclusion: The MR T2 values of the posterior meniscal horns increase with increasing age in women and are higher in women than in men. The age-related rise of T2 values appears to be more severe in medial menisci than in lateral menisci. Differences exist in the white zone and red/white zone.[[incitationindex]]SCI[[booktype]]電子
Global Constraints on Effective Dark Matter Interactions: Relic Density, Direct Detection, Indirect Detection, and Collider
An effective interaction approach is used to describe the interactions
between the spin 0 or spin 1/2 dark matter particle and the degrees of freedom
of the standard model. This approach is applicable to those models in which the
dark matter particles do not experience the standard-model interactions, e.g.,
hidden-sector models. We explore the effects of these effective interaction
operators on (i) dark matter relic density, (ii) spin-independent and
spin-dependent dark matter-nucleon scattering cross sections, (iii) cosmic
antiproton and gamma ray fluxes from the galactic halo due to dark matter
annihilation, and (iv) monojet and monophoton production plus missing energy at
the Tevatron and the Large Hadron Collider (LHC). We combine the experimental
data of relic density from WMAP7, spin-independent cross section from XENON100,
spin-dependent cross section from XENON10, ZEPLIN-III, and SIMPLE, cosmic
antiproton flux from PAMELA, cosmic gamma-ray flux from -LAT, and
the monojet and monophoton data from the Tevatron and the LHC, to put the most
comprehensive limits on each effective operator.Comment: 39 pages, 10 figures; a number of references added; a new section
about applicable models is added in the appendix; treatment of data sets are
modified; comments on LEP monophoton, FERMI-LAT dSphs data, and other
discussion. arXiv admin note: substantial text overlap with arXiv:1104.532
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV
We report a new STAR measurement of the longitudinal double-spin asymmetry
A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions
at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet
transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than
previous measurements. They provide significant new constraints on the gluon
spin contribution to the nucleon spin through the comparison to predictions
derived from one global fit of polarized deep-inelastic scattering
measurements.Comment: 7 pages, 4 figures + 1 tabl
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
Spin alignment measurements of the and vector mesons at RHIC
We present the first spin alignment measurements for the and
vector mesons produced at mid-rapidity with transverse momenta up
to 5 GeV/c at = 200 GeV at RHIC. The diagonal spin density
matrix elements with respect to the reaction plane in Au+Au collisions are
= 0.32 0.04 (stat) 0.09 (syst) for the
( GeV/c) and = 0.34 0.02 (stat) 0.03
(syst) for the ( GeV/c), and are constant with transverse
momentum and collision centrality. The data are consistent with the unpolarized
expectation of 1/3 and thus no evidence is found for the transfer of the
orbital angular momentum of the colliding system to the vector meson spins.
Spin alignments for and in Au+Au collisions were also measured
with respect to the particle's production plane. The result,
= 0.41 0.02 (stat) 0.04 (syst), is consistent with that in p+p
collisions, = 0.39 0.03 (stat) 0.06 (syst), also
measured in this work. The measurements thus constrain the possible size of
polarization phenomena in the production dynamics of vector mesons.Comment: 7 pages, 4 figures. fig.1 updated; one more reference added, one typo
corrected, published in PRC.77.06190
Hadronic resonance production in +Au collisions at = 200 GeV at RHIC
We present the first measurements of the , (892),
(1232), (1385), and (1520) resonances in +Au
collisions at = 200 GeV, reconstructed via their hadronic
decay channels using the STAR detector at RHIC. The masses and widths of these
resonances are studied as a function of transverse momentum (). We observe
that the resonance spectra follow a generalized scaling law with the transverse
mass (). The of , , and . The , ,
, , and ratios in
+Au collisions are compared to the measurements in minimum bias
interactions, where we observe that both measurements are comparable. The
nuclear modification factors () of the , , and
scale with the number of binary collisions () for 1.2 GeV/.Comment: STAR Collaboration. Submitted to PR
Enhanced strange baryon production in Au+Au collisions compared to p+p at sqrts = 200 GeV
We report on the observed differences in production rates of strange and
multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp
interactions at the same energy. The strange baryon yields in Au+Au collisions,
then scaled down by the number of participating nucleons, are enhanced relative
to those measured in pp reactions. The enhancement observed increases with the
strangeness content of the baryon, and increases for all strange baryons with
collision centrality. The enhancement is qualitatively similar to that observed
at lower collision energy sqrts =17.3 GeV. The previous observations are for
the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange
baryons even exceed binary scaling from pp yields.Comment: 7 pages, 4 figures. Printed in PR
- …