D. Drain

Neutron background measurements in the underground laboratory of Modane

Abstract Measurements of the background neutron environment, at a depth of 1780 m (4800 mwe) in the Underground Laboratory of Modane (L.S.M.) are reported. Using a 6 Li liquid scintillator, the energy spectrum of the fast neutron flux has been determined. Monte Carlo calculations of the (α, n ) and spontaneous fission processes in the surrounding rock has been performed and compared to the experimental result. In addition, using two 3 He neutron counters, the thermal neutron flux has been measured.

SICANE: A Detector array for the measurement of nuclear recoil quenching factors using a monoenergetic neutron beam

Abstract SICANE is a neutron scattering multidetector facility for the determination of the quenching factor (ratio of the response to nuclear recoils and to electrons) of cryogenic detectors used in direct WIMP searches. Well-collimated monoenergetic neutron beams are obtained with inverse (p,n) reactions. The facility is described, and results obtained for the quenching factors of scintillation in NaI(Tl) and of heat and ionization in Ge are presented.

Calibration of a CsI(Tl) crystal with nuclear recoils and pulse shape measurements for dark matter detection

Abstract The quenching factor of cesium and iodine nuclei recoiling in a CsI(Tl) scintillator is measured by scattering of 3 to 6 MeV neutrons. This factor increases when recoil energy decreases, from 7% at 150 keV to 15% at 25 keV. This relatively high efficiency could be useful in experiments dealing with very low recoil energies like the WIMP direct detection. These values are well explained by the Birks model. Pulse shape discrimination between electron and nuclei recoils is also investigated. Results are sufficiently good to allow a significant statistical rejection of radioactive background. This rejection capability is shown to be better than for NaI(Tl), at the same electron equivalent energy.

Dark matter search with a low temperature sapphire bolometer

Abstract A dark matter detection experiment using a low temperature 24 g sapphire bolometer is presented. The low radioactive background cryogenic facility, installed in a deep underground site, is described, as well as the low-noise read-out electronics and the data analysis. From the energy spectrum, measured down to 4 keV, exclusion plots are derived for WIMPs having coherent vector coupling or axial coupling to ordinary matter.

Status of the EDELWEISS experiment

Abstract The status of the EDELWEISS experiment, installed in the Frejus tunnel, is presented. In its first stage, the experiment uses a 70xa0g high purity Ge bolometer with heat-ionization discrimination. Based on physics data, gamma and neutron calibrations, the influence of inverse bias voltage (−2 and −6xa0V) on incomplete surface charge collection, which limits at present the performances of these detectors, is presented. Analysing runs with a total exposure of 1.17xa0kg×day after cuts, an upper limit of 0.6xa0event day kg keV at 90% confidence level in the 12–70xa0keV recoil energy interval is obtained. Planned upgrades are summarized.

Status and Outlook of the EDELWEISS Experiment

EDELWEISS is a direct search for WIMPs using cryogenic germanium ionizationphonon detectors and located in the Modane underground laboratory. We summarize the final results of the EDELWEISS I experiment obtained with up to nearly a kilogram of detectors. The increased exposure confirms previous results. We also report on the preparations for EDELWEISS II. Preliminary results are expected in 2006; the experiment could ultimately deploy up to 40 kg of detectors. Goals are to gain two orders of magnitude in sensitivity and to serve as a testbed for an even larger, tonne-scale, experiment.

LATEST RESULTS OF THE EDELWEISS EXPERIMENT

The EDELWEISS experiment is a direct detection Dark Matter Search, under the form of WIMPs. It uses heat and ionization Ge cryogenic detectors. We present the latest results obtained by the experiment with three new 320g bolometers. At present, EDELWEISS I is the most sensitive experiment for all WIMP masses compatible with accelerator constraints (Mwimp>30 GeV/c^2). We also briefly describe the status of the second stage EDELWEISS II involving initially 10 kg of detectors aiming a gain of two orders of magnitude in sensitivity.

Neutron scattering facility for the calibration of the response to nuclear recoils

A possibility to search for elementary particles as dark matter candidates is to detect elastic scattering with cryogenic detectors. For the interpretation of the data one has to determine the detector response to nuclear recoils, the so-called quenching factors. They can differ for the heat-, for the scintillation- and for the ionization-signal and can be measured by scattering of neutrons. The CRESST- and the EDELWEISS-collaborations have set up a neutron scattering facility for cryogenic detectors at the tandem-accelerator of the Munich ‘Maier-Leibniz-Labor.’ The scattering angle and the time-of-flight of the neutrons are measured by an array of liquid scintillator cells. The pulsed high energy (11 MeV) neutron beam is created by nuclear reaction of a 11B on a H2-gas target. The set-up and the results of first tests are presented.

DARK MATTER SEARCH IN THE EDELWEISS EXPERIMENT

Preliminary results obtained with 320g bolometers with simultaneous ionization and heat measurements are described. After a few weeks of data taking, data accumulated with one of these detectors are beginning to exclude the upper part of the DAMA region. Prospects for the present run and the second stage of the experiment, EDELWEISS-II, using an innovative reversed cryostat allowing data taking with 100 detectors, are briefly described.