233 research outputs found
A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope
The observation of a gamma-ray line in the cosmic-ray fluxes would be a
smoking-gun signature for dark matter annihilation or decay in the Universe. We
present an improved search for such signatures in the data of the Fermi Large
Area Telescope (LAT), concentrating on energies between 20 and 300 GeV. Besides
updating to 43 months of data, we use a new data-driven technique to select
optimized target regions depending on the profile of the Galactic dark matter
halo. In regions close to the Galactic center, we find a 4.6 sigma indication
for a gamma-ray line at 130 GeV. When taking into account the look-elsewhere
effect the significance of the observed excess is 3.2 sigma. If interpreted in
terms of dark matter particles annihilating into a photon pair, the
observations imply a dark matter mass of 129.8\pm2.4^{+7}_{-13} GeV and a
partial annihilation cross-section of = 1.27\pm0.32^{+0.18}_{-0.28}
x 10^-27 cm^3 s^-1 when using the Einasto dark matter profile. The evidence for
the signal is based on about 50 photons; it will take a few years of additional
data to clarify its existence.Comment: 23 pages, 9 figures, 3 tables; extended discussion; matches published
versio
Kuwait's marine biodiversity: Qualitative assessment of indicator habitats and species
The tropical waters of the Northern Arabian Gulf have a long history of maritime resource richness. High levels of biodiversity result from the complex matrix of coastal habitats, coral reefs and sea grass beds that characterise the region. Insight into the ongoing health of such habitats and the broader Kuwait maritime environment can be gauged by the status of indicator species found within these habitats. Here we review information on the occurrence, distribution and threats to key marine habitats and associated indicator species to provide an updated assessment of the state of the Kuwait's marine biodiversity. Critical evaluation of historic data highlights knowledge gaps needed inform the focus of future monitoring and conservation efforts. This assessment is designed to evaluate performance against environmental policy commitments, while providing a solid foundation for the design of comprehensive marine ecosystem management strategies
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
Principles to enable comprehensive national marine ecosystem status assessments from disparate data: The state of the marine environment in Kuwait
This paper presents an approach for preparing a comprehensive national marine ecosystem assessment and its application to the marine and coastal areas of the State of Kuwait. The approach is based on a set of principles to enable diverse data sources, of differing data quality and salience, to be combined into a single coordinated national assessment of marine ecosystem status to support the implementation of ecosystem-based management. The approach enables state assessments for multiple components of the marine ecosystem to be undertaken in a coordinated manner, using differing methods varying from quantitative to qualitative assessments depending on data and indicator availability. The marine ecosystem assessment is structured according to 6 major themes: i) Biodiversity, ii) Commercial Fisheries, iii) Food and Water Quality for Human Health, iv) Environmental Pollution, v) Eutrophication and Harmful Algal Blooms, and vi) Coastal Process and Oceanography. Comprehensive ecosystem assessments are an essential part of implementing the ecosystem approach, however detailed data directly related to clear, specified numerical management targets covering all aspects of a marine ecosystem are rarely available. The development of a State of the Marine Environment Report (SOMER) for Kuwait demonstrate that a coordinated comprehensive ecosystem assessment can be conducted using disparate data, and in relation to partially specified regulatory management objectives. The Kuwait SOMER highlighted the issues of coastal pollution, particularly sewage for human health and the environment. It shows that the rapid urbanization of Kuwait has led to significant changes in the ecology, with clear impacts on coral reef health, the availability of nesting locations for turtles and habitats for migratory birds. Long-term changes in nutrient input, via waste water and modified freshwater inputs is resulting in demonstrable impacts on a range of marine species and habitats within Kuwait marine waters. It also supports the move towards a regional approach required due to transboundary properties of many of the ecosystem components, drivers and pressures
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
MO analysis of the high statistics Belle results on with chiral constraints
We reconsider Muskhelishvili-Omn\`es (MO) dispersive representations of
photon-photon scattering to two pions, motivated by the very high statistics
results recently released by the Belle collaboration for charged as well as
neutral pion pairs and also by recent progress in the determination of the
low-energy scattering amplitude. Applicability of this formalism is
extended beyond 1 GeV by taking into account inelasticity due to . A
modified MO representation is derived which has the advantage that all
polynomial ambiguities are collected into the subtraction constants and have
simple relations to pion polarizabilities. It is obtained by treating
differently the exactly known QED Born term and the other components of the
left-hand cut. These components are approximated by a sum over resonances. All
resonances up to spin two and masses up to GeV are included. The
tensor contributions to the left-hand cut are found to be numerically
important. We perform fits to the data imposing chiral constraints, in
particular, using a model independent sum rule result on the chiral
coupling . Such theoretical constraints are necessary because the
experimental errors are dominantly systematic. Results on further
couplings and pion dipole and quadrupole polarizabilities are then derived from
the fit. The relevance of the new data for distinguishing between two possible
scenarios of isospin breaking in the region is discussed.Comment: 44 pages, 12 figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
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