P. Charvin

Improved exclusion limits from the edelweiss wimp search

Abstract The EDELWEISS experiment has improved its sensitivity for the direct search for WIMP dark matter. In the recoil energy range relevant for WIMP masses below 10xa0TeV/ c 2 , no nuclear recoils were observed in the fiducial volume of a heat-and-ionization cryogenic Ge detector operated in the low-background environment of the Laboratoire Souterrain de Modane in the Frejus Tunnel, during an effective exposure ofxa07.4xa0kgxa0d. This result is combined with the previous EDELWEISS data to derive a limit on the cross-section for spin-independent interaction of WIMPs and nucleons as a function of WIMP mass, using standard nuclear physics and astrophysical assumptions. This limit excludes at more than 99.8%xa0CL a WIMP candidate with a mass of 44xa0GeV/ c 2 and a cross-section of 5.4×10 −6 xa0pb, as reported by the DAMA Collaboration. A first sample of supersymmetric models are also excluded atxa090% CL.

First results of the EDELWEISS WIMP search using a 320 g heat-and-ionization Ge detector

The EDELWEISS collaboration has performed a direct search for WIMP dark matter using a 320 g heat-and-ionization cryogenic Ge detector operated in a low-background environment in the Laboratoire Souterrain de Modane. No nuclear recoils are observed in the fiducial volume in the 30-200 keV energy range during an effective exposure of 4.53 kg.days. Limits for the cross-section for the spin-independent interaction of WIMPs and nucleons are set in the framework of the Minimal Supersymmetric Standard Model (MSSM). The central value of the signal reported by the experiment DAMA is excluded at 90% CL.

Calibration of the EDELWEISS cryogenic heat-and-ionization germanium detectors for dark matter search

Several aspects of the analysis of the data obtained with the cryogenic heat-and-ionization Ge detectors used by the EDELWEISS dark matter search experiment are presented. Their calibration, the determination of their energy threshold, fiducial volume and nuclear recoil acceptance are detailed.

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 kgxa0day 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 eventxa0day−1xa0kg−1xa0keVrecoil−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.

Event categories in the EDELWEISS WIMP search experiment

Four categories of events have been identified in the EDELWEISS-I dark matter experiment using germanium cryogenic detectors measuring simultaneously charge and heat signals. These categories of events are interpreted as electron and nuclear interactions occurring in the volume of the detector, and electron and nuclear interactions occurring close to the surface of the detectors (within ≈10–20 μm of the surface). We discuss the hypothesis that low energy surface nuclear recoils, which seem to have been unnoticed by previous WIMP searches, may provide an interpretation of the anomalous events recorded by the UKDMC and Saclay NaI experiments. The present analysis points to the necessity of taking into account surface nuclear and electron recoil interactions for a reliable estimate of background rejection factors.

STATUS OF THE EDELWEISS EXPERIMENT

Abstract The status of the EDELWEISS experiment is presented. First tests of a prototype detector of the “1xa0kg” stage show an event rate before rejection of ≈2xa0evt/kg/keV/day above E >20xa0keV, a factor ≈10 improvement compared to previous runs. An unexpected category of events is evidenced and used to interpret the “bump” events observed by the UKDMC and Saclay NaI WIMP detection experiments. Finally, the short-term perspectives of the “1xa0kg” stage, which should allow to sample realistic SUSY models, and the main characteristics of the EDELWEISS-II experiment are described.

Looking for SUSY with EDELWEISS-I and -II

The latest results obtained by the EDELWEISS WIMP (weakly interacting massive particles) direct detection experiment using three heat-and-ionization 320-g germanium bolometers are given. Presently the most sensitive WIMP direct detection experiment for WIMP mass >30 GeV, EDELWEISSI is testing a first region of SUSY models compatible with accelerator constraints. The status and main characteristics of EDELWEISS-II, involving in a first stage 28 germanium bolometers and able to accommodate up to 120 detectors, are briefly presented, together with neutron background estimates.

Dark Matter Search in the EDELWEISS Experiment

Abstract The EDELWEISS collaboration is performing a direct search for WIMP dark matter in a low-background environment in the Laboratoire Souterrain de Modane. Two series of results obtained with 320 g heat-and-ionization detectors are presented. During the 4.53 effective exposure of the year 2000 run, no nuclear events are observed in the fiducial volume in the 30–200 keV energy range. The central value of the signal reported by the DAMA experiment NaI1–4 is thus excluded at 90% CL. The present 2002 setup with three detectors is described and improved calibration performances are presented. The R&D program and the EDELWEISS-II stage of the experiment are also briefly described.

The EDELWEISS Experiment: Status and Outlook

The EDELWEISS Dark Matter search uses low-temperature Ge detectors with heat and ionisation read-out to identify nuclear recoils induced by elastic collisions with WIMPs from the galactic halo. Results from the operation of 70 g and 320 g Ge detectors in the low-background environment of the Modane Underground Laboratory (LSM) are presented.