Paper

Background studies for the EDELWEISS dark matter experiment

Filosofov, D, Schmidt, B, Sanglard, V, Weber, M, Blümer, J, Rozov, S, Domange, J, Walker, R J, Fourches, N, Torrento-Coello, A S, Couedo, F, Holtzer, N, Rigaut, O, Charlieux, F, Siebenborn, B, Juillard, A, Kozlov, V, Bergé, L, Broniatowski, A, Robinson, M, Kudryavtsev, V A, De Jesus, M, Henry, S, Pari, P, Kluck, H, Nones, C, Benoît, A, Vagneron, L, Tcherniakhovski, D, Cox, G A, Augier, C, X-F Navick, Kraus, H, H Le Sueur, Semikh, S, Coulter, P, Gerbier, G, Olivieri, E, Kleifges, M, Scorza, S, Brudanin, V, Bergmann, T, Censier, B, Marnieros, S, Loaiza, P, Hervé, S, Zhang, X, Heuermann, G, Eitel, K, Gascon, J, Chapellier, M, Armengaud, E, Dumoulin, L, Paul, B, Yakushev, E, A -A Drilien, Gros, M, Menshikov, A

2013

Overview

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.

• Publisher: Cornell University Library, arXiv.org
• Subject: Background radiation / Computer simulation / Cross-sections / Dark matter / Gamma rays / Mathematical analysis / Neutrons / Purity / Radioactivity / Recoil / Shielding / Weakly interacting massive particles