/ physics.ins-det arXiv:1305.3628

Background studies for the EDELWEISS dark matter experiment

Armengaud, E. (DAPNIA, Saclay) ; Augier, C. (Lyon, IPN) ; Benoit, A. (LPSC, Grenoble) ; Benoit, A. (Lyon, IPN) ; Berge, L. (CSNSM, Orsay) ; Bergmann, T. (Karlsruhe, Inst. Technol.) ; Blumer, J. (Karlsruhe, Inst. Technol.) ; Broniatowski, A. (CSNSM, Orsay) ; Brudanin, V. (Dubna, JINR) ; Censier, B. (Lyon, IPN) ; Chapellier, M. (CSNSM, Orsay) ; Charlieux, F. (Lyon, IPN) ; Couedo, F. (CSNSM, Orsay) ; Coulter, P. (Oxford U.) ; Cox, G.A. (Karlsruhe U., EKP) ; De Jesus, M. (Lyon, IPN) ; Domange, J. (DAPNIA, Saclay) ; Drilien, A.A. (CSNSM, Orsay) ; Dumoulin, L. (CSNSM, Orsay) ; Eitel, K. (Karlsruhe, Inst. Technol.) ; Filosofov, D. (Dubna, JINR) ; Fourches, N. (DAPNIA, Saclay) ; Gascon, J. (Lyon, IPN) ; Gerbier, G. (DAPNIA, Saclay) ; Gros, M. (DAPNIA, Saclay) ; Henry, S. (Oxford U.) ; Herve, S. (DAPNIA, Saclay) ; Heuermann, G. (Karlsruhe U., EKP) ; Holtzer, N. (CSNSM, Orsay) ; Juillard, A. (Lyon, IPN) ; Kleifges, M. (Karlsruhe, Inst. Technol.) ; Kluck, H. (Karlsruhe U., EKP) ; Kozlov, V. (Karlsruhe, Inst. Technol.) ; Kraus, H. (Oxford U.) ; Kudryavtsev, V.A. (Sheffield U.) ; Le Sueur, H. (CSNSM, Orsay) ; Loaiza, P. (Carleton U.) ; Marnieros, S. (CSNSM, Orsay) ; Menshikov, A. (Karlsruhe, Inst. Technol.) ; Navick, X-F. (DAPNIA, Saclay) ; Nones, C. (DAPNIA, Saclay) ; Olivieri, E. (CSNSM, Orsay) ; Pari, P. (IRAMIS, Saclay) ; Paul, B. (DAPNIA, Saclay) ; Rigaut, O. (CSNSM, Orsay) ; Robinson, M. (Sheffield U.) ; Rozov, S. (Dubna, JINR) ; Sanglard, V. (Lyon, IPN) ; Schmidt, B. (Karlsruhe U., EKP) ; Scorza, S. (Lyon, IPN) ; Siebenborn, B. (Karlsruhe, Inst. Technol.) ; Semikh, S. (Dubna, JINR) ; Tcherniakhovski, D. (Karlsruhe, Inst. Technol.) ; Torrento-Coello, A.S. (DAPNIA, Saclay) ; Vagneron, L. (Lyon, IPN) ; Walker, R.J. (Karlsruhe U., EKP) ; Weber, M. (Karlsruhe, Inst. Technol.) ; Yakushev, E. (Dubna, JINR) ; Zhang, X. (Oxford U.)

Pages: 15

Abstract: 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.

Keyword(s): Dark matter ; WIMPs ; Background radiation ; Radioactivity ; The EDELWEISS experiment

Web-Page: http://inspirehep.net/record/1233696/files/mult-pe-u-final.png; http://inspirehep.net/record/1233696/files/nsp-pe-u-new.png; http://inspirehep.net/record/1233696/files/nsp-source.png; http://inspirehep.net/record/1233696/files/nsp-ss.png; http://inspirehep.net/record/1233696/files/plot_alle_c_juin2012.png; http://inspirehep.net/record/1233696/files/plot_le_20_200_juin2012_b.png; http://inspirehep.net/record/1233696/files/qplot-ss-u-final.png; http://inspirehep.net/record/1233696/files/setup.png; http://inspirehep.net/record/1233696/files/zoom.png; http://inspirehep.net/record/1233696/files/arXiv%3A1305.3628.pdf

Note: *Temporary entry*; 15 pages, 9 figures, to be published in Astroparticle Physics

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