Background discrimination capabilities of a heat and ionization germanium cryogenic detector |
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| Authors: | EDELWEISS Collaboration P Di Stefano L Berg B Chambon M Chapellier J Chaumont G Chardin P Charvin M De Jsus D Drain L Dumoulin P Forget P Garoche J Gascon C Goldbach D L'Hte J Mallet J Mangin S Marnieros L Miramonti L Mosca X-F Navick G Nollez P Pari S Pcourt E Simon L Stab J-P Torre R Tourbot D Yvon |
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| Institution: | a CEA, Centre d'Etudes Nucléaires de Saclay, DSM/DAPNIA, F-91191 Gif-sur-Yvette Cedex, France;b CSNSM, IN2P3-CNRS, Université Paris XI, bât. 108, F-91405 Orsay Cedex, France;c IPN Lyon and UCBL, IN2P3-CNRS, 43 Bd. du 11 novembre 1918, F-69622 Villeurbanne Cedex, France;d CEA, Centre d'Etudes Nucléaires de Saclay, DSM/DRECAM, F-91191 Gif-sur-Yvette Cedex, France;e Laboratoire Souterrain de Modane, CEA-CNRS, 90 rue Polset, F-73500 Modane, France;f Laboratoire de Physique des Solides, Université Paris XI, F-91405 Orsay Cedex, France;g Institut d'Astrophysique de Paris, INSU-CNRS, 98 bis Bd. Arago, F-75014 Paris, France;h LPUB, Université de Bourgogne, F-21078 Dijon, France;i Institut de Physique Nucléaire, Université Paris XI, F-91405 Orsay Cedex, France;j Service d'Aéronomie, BP 3, F-91371 Verrières le Buisson Cedex, France |
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| Abstract: | The discrimination capabilities of a 70 g heat and ionization Ge bolometer are studied. This first prototype has been used by the EDELWEISS dark matter experiment, installed in the Laboratoire Souterrain de Modane, for direct detection of WIMPs. Gamma and neutron calibrations demonstrate that this type of detector is able to reject more than 99.6% of the background while retaining 95% of the signal, provided that the background events distribution is not biased towards the surface of the Ge crystal. However, the 1.17 kg day of data taken in a relatively important radioactive environment show an extra population slightly overlapping the signal. This background is likely due to interactions of low energy photons or electrons near the surface of the crystal, and is somewhat reduced by applying a higher charge-collecting inverse bias voltage (−6 V instead of −2 V) to the Ge diode. Despite this contamination, more than 98% of the background can be rejected while retaining 50% of the signal. This yields a conservative upper limit of 0.7 event day−1 kg−1 keVrecoil−1 at 90% confidence level in the 15–45 keV recoil energy interval; the present sensitivity appears to be limited by the fast ambient neutrons. Upgrades in progress on the installation are summarized. |
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| Keywords: | Dark matter WIMP Cryogenic detector |
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