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25 April 2024

» arxiv » 1305.3628

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Background studies for the EDELWEISS dark matter experiment
E. Armengaud ; C. Augier ; A. Beno^it ; A. Beno^it ; L. Bergé ; T. Bergmann ; J. Blümer ; A. Broniatowski ; V. Brudanin ; B. Censier ; M. Chapellier ; F. Charlieux ; F. Couedo ; P. Coulter ; G.A. Cox ; M. De Jesus ; J. Domange ; A.-A. Drilien ; L. Dumoulin ; K. Eitel ; D. Filosofov ; N. Fourches ; J. Gascon ; G. Gerbier ; M. Gros ; S. Henry ; S. Hervé ; G. Heuermann ; N. Holtzer ; A. Juillard ; M. Kleifges ; H. Kluck ; V. Kozlov ; H. Kraus ; V.A. Kudryavtsev ; H. Le Sueur ; P. Loaiza ; S. Marnieros ; A. Menshikov ; X-F. Navick ; C. Nones ; E. Olivieri ; P. Pari ; B. Paul ; O. Rigaut ; M. Robinson ; S. Rozov ; V. Sanglard ; B. Schmidt ; S. Scorza ; B. Siebenborn ; S. Semikh ; D. Tcherniakhovski ; A.S. Torrento-Coello ; L. Vagneron ; R.J. Walker ; M. Weber ; E. Yakushev ; X. Zhang ;
Date:	15 May 2013
Abstract:	The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter using cryogenic Ge detectors (400 g each) and 384 kg$ imes$days of effective exposure. A cross-section of $4.4 imes 10^{-8}$ 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 $ imes10^{-9}$ 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 ($le0.9$), surface betas ($le0.3$), and muon-induced neutrons ($le0.7$), 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.
Source:	arXiv, 1305.3628
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