Background studies for the EDELWEISS dark matter experiment
Creators: name: Armengaud, E.
name: Augier, C.
name: Benoît, A.
name: Benoît, A.
name: Bergé, L.
name: Bergmann, T.
name: Blümer, J.
name: Broniatowski, A.
name: Brudanin, V.
name: Censier, B.
name: Chapellier, M.
name: Charlieux, F.
name: Couedo, F.
name: Coulter, P.
name: Cox, G. A.
name: De Jesus, M.
name: Domange, J.
name: Drilien, A. -A.
name: Dumoulin, L.
name: Eitel, K.
name: Filosofov, D.
name: Fourches, N.
name: Gascon, J.
name: Gerbier, G.
name: Gros, M.
name: Henry, S.
name: Hervé, S.
name: Heuermann, G.
name: Holtzer, N.
name: Juillard, A.
name: Kleifges, M.
name: Kluck, H.
name: Kozlov, V.
name: Kraus, H.
name: Kudryavtsev, V. A.
name: Sueur, H. Le
name: Loaiza, P.
name: Marnieros, S.
name: Menshikov, A.
name: Navick, X-F.
name: Nones, C.
name: Olivieri, E.
name: Pari, P.
name: Paul, B.
name: Rigaut, O.
name: Robinson, M.
name: Rozov, S.
name: Sanglard, V.
name: Schmidt, B.
name: Scorza, S.
name: Siebenborn, B.
name: Semikh, S.
name: Tcherniakhovski, D.
name: Torrento-Coello, A. S.
name: Vagneron, L.
name: Walker, R. J.
name: Weber, M.
name: Yakushev, E.
name: Zhang, X.
Publisher: name: arXiv
Year: 2013
Subjects: subject: Instrumentation and Detectors (physics.ins-det)
subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter using cryogenic Ge detectors (400 g each) and 384 kg$\times$days of effective exposure. A cross-section of $4.4 \times 10^{-8}$ 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 $\times10^{-9}$ 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.
description: 15 pages, 9 figures, to be published in Astroparticle Physics