| P. Di Stefano, L. Berge, B. Chambon, M. Chapellier, J. Chaumont, G. Chardin, P. Charvin, M. De Jesus, D. Drain, L. Dumoulin, P. Forget, P. Garoche, J. Gascon, C. Goldbach, D. L'Hote, J. Mallet, J. Mangin, S. Marnieros, L. Miramonti, L. Mosca, X.-F. Navick, G. Nollez, P. Pari, S. Pecourt, E. Simon, L. Stab, J.-P. Torre, R. Tourbot, D. Yvon |
Abstract:
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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.
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