A dedicated analysis of the muon-induced background in the EDELWEISS dark matter search has been performed on a data set acquired in 2009 and 2010. The total muon flux underground in the Laboratoire ...Souterrain de Modane (LSM) was measured to be Φμ=(5.4±0.2-0.9+0.5)muons/m2/d. The modular design of the μ-veto system allows the reconstruction of the muon trajectory and hence the determination of the angular dependent muon flux in LSM. The results are in good agreement with both MC simulations and earlier measurements. Synchronization of the μ-veto system with the phonon and ionization signals of the Ge detector array allowed identification of muon-induced events. Rates for all muon-induced events Γμ=(0.172±0.012)evts/(kgd) and of WIMP-like events Γμ–n=0.008-0.004+0.005evts/(kgd) were extracted. After vetoing, the remaining rate of accepted muon-induced neutrons in the EDELWEISS-II dark matter search was determined to be Γirredμ–n<6·10-4evts/(kgd) at 90% C.L. Based on these results, the muon-induced background expectation for an anticipated exposure of 3000kgd for EDELWEISS-III is N3000kgdμ–n<0.6 events.
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 γ-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 4.4×10−8 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.
Muon-induced neutrons constitute a prominent background component in a number of low count rate experiments, namely direct searches for dark matter. In this work we describe a neutron detector to ...measure this background in an underground laboratory, the Laboratoire Souterrain de Modane. The system is based on 1
m
3 of Gd-loaded scintillator and it is linked with the muon veto of the EDELWEISS-II experiment for coincident muon detection. The system was installed in autumn 2008 and passed since then a number of commissioning tests proving its full functionality. The data-taking is continuously ongoing and a count rate of the order of 1 muon-induced neutron per day has been achieved.
The EDELWEISS-II Collaboration has performed a direct search for WIMP dark matter with an array of ten 400 g heat-and-ionization cryogenic detectors equipped with interleaved electrodes for the ...rejection of near-surface events. Six months of continuous operation at the Laboratoire Souterrain de Modane have been achieved. The observation of one nuclear recoil candidate above 20 keV in an effective exposure of 144 kg d is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 1.0×10−7 pb is excluded at 90% CL for a WIMP mass of 80 GeV/c2. This result demonstrates for the first time the very high background rejection capabilities of these simple and robust detectors in an actual WIMP search experiment.
The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter using cryogenic Ge detectors (400g each) and 384kg×days of effective exposure. A cross-section of 4.4×10-8pb is ...excluded at 90% C. L. for a WIMP mass of 85GeV. The next phase, EDELWEISS-III, aims to probe spin-independent WIMP-nucleon cross-sections down to a few ×10-9pb. 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 20–200keV 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 20–200keV in the EDELWEISS-II data together with the expected upper limit on the misidentified gamma-ray events (⩽0.9), surface betas (⩽0.3), and muon-induced neutrons (⩽0.7), do not contradict five observed events in nuclear recoil band. We have then extended the simulation framework to the EDELWEISS-III configuration with 800g crystals, better material purity and additional neutron shielding inside the cryostat. The gamma-ray and neutron backgrounds in 24kg 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.
A multi-tiered data structure, analysis toolkit and data processing management system has been constructed using ROOT and CouchDB. This system is well suited for experiments that acquire many ...computer files of raw data over the course of months or years, that are distributed to different computing centers and further reduced in size by several steps of data processing. Data handling for experiments searching for rare events extracted from digitized pulse traces typically fit this description. An implementation of this system has been constructed for the EDELWEISS-III experiment and is described here in some detail. This solution may also serve as a prototype system for the proposed EURECA experiment.
A dedicated analysis of the muon-induced background in the EDELWEISS dark matter search has been performed on a data set acquired in 2009 and 2010. The total muon flux underground in the Laboratoire ...Souterrain de Modane (LSM) was measured to be \(\Phi_{\mu}=(5.4\pm 0.2 ^{+0.5}_{-0.9})\)\,muons/m\(^2\)/d. The modular design of the muon-veto system allows the reconstruction of the muon trajectory and hence the determination of the angular dependent muon flux in LSM. The results are in good agreement with both MC simulations and earlier measurements. Synchronization of the muon-veto system with the phonon and ionization signals of the Ge detector array allowed identification of muon-induced events. Rates for all muon-induced events \(\Gamma^{\mu}=(0.172 \pm 0.012)\, \rm{evts}/(\rm{kg \cdot d})\) and of WIMP-like events \(\Gamma^{\mu-n} = 0.008^{+0.005}_{-0.004}\, \rm{evts}/(\rm{kg \cdot d})\) were extracted. After vetoing, the remaining rate of accepted muon-induced neutrons in the EDELWEISS-II dark matter search was determined to be \(\Gamma^{\mu-n}_{\rm irred} < 6\cdot 10^{-4} \, \rm{evts}/(\rm{kg \cdot d})\) at 90%\,C.L. Based on these results, the muon-induced background expectation for an anticipated exposure of 3000\,\kgd\ for EDELWEISS-3 is \(N^{\mu-n}_{3000 kg\cdot d} < 0.6\) events.
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. Using an exposure of 113 kg.d, we find no evidence for an exponential distribution of low-energy nuclear recoils that could be attributed to WIMP elastic scattering. For WIMPs of mass 10 GeV, the observation of one event in the WIMP search region results in a 90% CL limit of 1.0 \times 10^-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.
The AMS experiment Torrentó Coello, A. S.
Neutrinos and Explosive Events in the Universe
Book Chapter
AMS is a particle physics detector which will operate on the International Space Station (ISS) for at least 3 years, to search for cosmic antimatter and dark matter signatures, to make a deep study ...of cosmic ray composition and energy spectrum and to do some gamma ray astrophysics. The detector design and its placement for a long period of time in a background-free environment will make possible a high precision and high statistics data collection, allowing a significant improvement of present results on that issues.
The EDELWEISS-II collaboration has performed a direct search for WIMP dark matter with an array of ten 400-g heat-and-ionization cryogenic detectors equipped with Inter-Digit electrodes for the ...rejection of near-surface events. Results from one year of continuous operation at the Laboratoire Souterrain de Modane will be presented. A sensitivity to the spin-independent WIMP-nucleon elastic cross-section of 4.4x10^{-8} pb was achieved using a 384 kgd effective exposure. We also interpret the results in the inelastic scattering scenario, excluding the DAMA allowed region for WIMP masses greater than 90 GeV for a mass splitting of 120 keV. The results obtained demonstrate the excellent background rejection capabilities of these simple and robust detectors in an actual WIMP search experiment. Some first results with 800-g detectors will be also presented together with the prospects for this experiment and the ton-scale EURECA project.
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