Background discrimination capabilities of a heat and ionization germanium cryogenic detector

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}.keV^{-1}_{recoil} 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.

Submitted to Astroparticle Physics, 14 pages

References in corpus (7)

• Possible Gravitational Microlensing of a Star in the Large Magellanic Cloud
• EROS and MACHO Combined Limits on Planetary Mass Dark Matter in the Galactic Halo
• Discrimination between Nuclear Recoils and Electron Recoils by Simultaneous Detection of Phonons and Scintillation Light
• New limits on dark--matter WIMPs from the Heidelberg--Moscow experiment
• Event categories in the EDELWEISS WIMP search experiment
• High-purity germanium detector ionization pulse shapes of nuclear recoils, gamma interactions and microphonism
• Status of the EDELWEISS Experiment

Cited by in corpus (10)

• Improved Exclusion Limits from the EDELWEISS WIMP Search
• Final results of the EDELWEISS-I dark matter search with cryogenic heat-and-ionization Ge detectors
• First Results of the EDELWEISS WIMP Search using a 320 g Heat-and-Ionization Ge Detector
• Background studies for the EDELWEISS dark matter experiment
• Neutron beam test of CsI crystal for dark matter search
• Muon-induced background in the EDELWEISS dark matter search
• Calibration of the EDELWEISS Cryogenic Heat-and-ionisation Germanium Detectors for Dark Matter Search
• Low-background applications of MICROMEGAS detector technology
• EDELWEISS-II : Status and future
• The EDELWEISS Experiment : Status and Outlook