622 research outputs found
Angular Power Spectrum Estimation of Cosmic Ray Anisotropies with Full or Partial Sky Coverage
We study the angular power spectrum estimate in order to search for large
scale anisotropies in the arrival directions distribution of the highest-energy
cosmic rays. We show that this estimate can be performed even in the case of
partial sky coverage and validated over the full sky under the assumption that
the observed fluctuations are statistically spatial stationary. If this
hypothesis - which can be tested directly on the data - is not satisfied, it
would prove, of course, that the cosmic ray sky is non isotropic but also that
the power spectrum is not an appropriate tool to represent its anisotropies,
whatever the sky coverage available. We apply the method to simulations of the
Pierre Auger Observatory, reconstructing an input power spectrum with the
Southern site only and with both Northern and Southern ones. Finally, we show
the improvement that a full-sky observatory brings to test an isotropic
distribution, and we discuss the sensitivity of the Pierre Auger Observatory to
large scale anisotropies.Comment: 16 pages, 6 figures, version accepted for publication by JCA
The IAXO Helioscope
Çetin, Serkant Ali (Dogus Author) -- Conference full title: 7th International Symposium on Large TPCs for Low-Energy Rare Event Detection; Institute of Astroparticle Physics (APC) Campus - Paris Diderot UniversityParis; France; 15 December 2014 through 17 December 2014The IAXO (International Axion Experiment) is a fourth generation helioscope with a sensitivity, in terms of detectable signal counts, at least 104 better than CAST phase-I, resulting in sensitivity on gaγ one order of magnitude better. To achieve this performance IAXO will count on a 8-coil toroidal magnet with 60 cm diameter bores and equipped with X-ray focusing optics into 0.20 cm2 spots coupled to ultra-low background Micromegas X-ray detectors. The magnet will be on a platform that will allow solar tracking for 12 hours per day. The next short term objectives are to prepare a Technical Design Report and to construct the first prototypes of the hardware main ingredients: demonstration coil, X-ray optics and low background detector while refining the physics case and studying the feasibility studies for Dark Matter axions
The Deinococcus radiodurans DR1245 Protein, a DdrB Partner Homologous to YbjN Proteins and Reminiscent of Type III Secretion System Chaperones
The bacterium Deinococcus radiodurans exhibits an extreme resistance to ionizing radiation. A small subset of Deinococcus genus-specific genes were shown to be up-regulated upon exposure to ionizing radiation and to play a role in genome reconstitution. These genes include an SSB-like protein called DdrB. Here, we identified a novel protein encoded by the dr1245 gene as an interacting partner of DdrB. A strain devoid of the DR1245 protein is impaired in growth, exhibiting a generation time approximately threefold that of the wild type strain while radioresistance is not affected. We determined the three-dimensional structure of DR1245, revealing a relationship with type III secretion system chaperones and YbjN family proteins. Thus, DR1245 may display some chaperone activity towards DdrB and possibly other substrates. © 2013 Norais et al
Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes
The EDELWEISS-II collaboration has completed a direct search for WIMP dark
matter with an array of ten 400-g cryogenic germanium detectors in operation at
the Laboratoire Souterrain de Modane. The combined use of thermal phonon
sensors and charge collection electrodes with an interleaved geometry enables
the efficient rejection of gamma-induced radioactivity as well as near-surface
interactions. A total effective exposure of 384 kg.d has been achieved, mostly
coming from fourteen months of continuous operation. Five nuclear recoil
candidates are observed above 20 keV, while the estimated background is 3.0
events. The result is interpreted in terms of limits on the cross-section of
spin-independent interactions of WIMPs and nucleons. A cross-section of
4.4x10^-8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints
are also set on models where the WIMP-nucleon scattering is inelastic.Comment: 23 pages, 5 figures; matches published versio
A search for low-mass WIMPs with EDELWEISS-II heat-and-ionization detectors
We report on a search for low-energy (E < 20 keV) WIMP-induced nuclear
recoils using data collected in 2009 - 2010 by EDELWEISS from four germanium
detectors equipped with thermal sensors and an electrode design (ID) which
allows to efficiently reject several sources of background. The data indicate
no evidence for an exponential distribution of low-energy nuclear recoils that
could be attributed to WIMP elastic scattering after an exposure of 113 kg.d.
For WIMPs of mass 10 GeV, the observation of one event in the WIMP search
region results in a 90% CL limit of 1.0x10^-5 pb on the spin-independent
WIMP-nucleon scattering cross-section, which constrains the parameter space
associated with the findings reported by the CoGeNT, DAMA and CRESST
experiments.Comment: PRD rapid communication accepte
Aperture calculation of the Pierre Auger Observatory surface detector
We determine the instantaneous aperture and integrated exposure of the
surface detector of the Pierre Auger Observatory, taking into account the
trigger efficiency as a function of the energy, arrival direction (with zenith
angle lower than 60 degrees) and nature of the primary cosmic-ray. We make use
of the so-called Lateral Trigger Probability function (or LTP) associated with
an extensive air shower, which summarizes all the relevant information about
the physics of the shower, the water tank Cherenkov detector, and the triggers.Comment: Proc. of the 29th ICRC (Pune, India), LaTeX, 4 pages, 5 figure
Background studies for the EDELWEISS dark matter experiment
The EDELWEISS-II collaboration has completed a direct search for WIMP dark
matter using cryogenic Ge detectors (400 g each) and 384 kgdays of
effective exposure. A cross-section of pb is excluded at
90% C.L. for a WIMP mass of 85 GeV. The next phase, EDELWEISS-III, aims to
probe spin-independent WIMP-nucleon cross-sections down to a few
pb. We present here the study of gamma and neutron background
coming from radioactive decays in the set-up and shielding materials. We have
carried out Monte Carlo simulations for the completed EDELWEISS-II setup with
GEANT4 and normalised the expected background rates to the measured
radioactivity levels (or their upper limits) of all materials and components.
The expected gamma-ray event rate in EDELWEISS-II at 20-200 keV agrees with the
observed rate of 82 events/kg/day within the uncertainties in the measured
concentrations. The calculated neutron rate from radioactivity of 1.0-3.1
events (90% C.L.) at 20-200 keV in the EDELWEISS-II data together with the
expected upper limit on the misidentified gamma-ray events (), surface
betas (), and muon-induced neutrons (), do not contradict 5
observed events in nuclear recoil band. We have then extended the simulation
framework to the EDELWEISS-III configuration with 800 g crystals, better
material purity and additional neutron shielding inside the cryostat. The
gamma-ray and neutron backgrounds in 24 kg fiducial mass of EDELWEISS-III have
been calculated as 14-44 events/kg/day and 0.7-1.4 events per year,
respectively. The results of the background studies performed in the present
work have helped to select better purity components and improve shielding in
EDELWEISS-III to further reduce the expected rate of background events in the
next phase of the experiment.Comment: 15 pages, 9 figures, to be published in Astroparticle Physic
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