A. de Lesquen

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.

Identification of backgrounds in the EDELWEISS-I dark matter search experiment

Abstract This paper presents our interpretation and understanding of the different backgrounds in the EDELWEISS-I data sets. We analyze in detail the several populations observed, which include gammas, alphas, neutrons, thermal sensor events and surface events, and try to combine all data sets to provide a coherent picture of the nature and localization of the background sources. In light of this interpretation, we draw conclusions regarding the background suppression scheme for the EDELWEISS-II phase.

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.

EURECA — the European future of cryogenic dark matter searches

EURECA (European Underground Rare Event Calorimeter Array) is a new project, searching for dark matter, with largely the present groups of the CRESST and EDELWEISS experiments and already a few new groups. The aim is to explore scalar cross sections in the 10−9 - 10−10 pico-barn region with a target mass of up to one tonne. A major advantage of EURECA is our planned use of more that just one target material (multi target experiment for WIMP identification). In preparation for this large-scale experiment, R&D for EURECA is provided through the current phases of CRESST and EDELWEISS.

Sensitivity of the EDELWEISS WIMP search to spin-dependent interactions

The EDELWEISS collaboration is searching for WIMP dark matter using natural Ge cryogenic detectors. The whole data set of the first phase of the experiment contains a fiducial exposure of 4.8 kg.day on Ge-73, the naturally present (7.8%), high-spin Ge isotope. The sensitivity of the experiment to the spin-dependent WIMP-nucleon interactions is evaluated using the model-independent framework proposed by Tovey et al.

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.

Measurement of the response of heat-and-ionization germanium detectors to nuclear recoils

Abstract The heat quenching factor Q ′ (the ratio of the heat signals produced by nuclear and electron recoils of equal energy) of the heat-and-ionization germanium bolometers used by the EDELWEISS collaboration has been measured. It is explained how this factor affects the energy scale and the effective quenching factor observed in calibrations with neutron sources. This effective quenching effect is found to be equal to Q / Q ′ , where Q is the quenching factor of the ionization yield. To measure Q ′ , a precise EDELWEISS measurement of Q / Q ′ is combined with values of Q obtained from a review of all available measurements of this quantity in tagged neutron beam experiments. The systematic uncertainties associated with this method to evaluate Q ′ are discussed in detail. For recoil energies between 20 and 100xa0keV, the resulting heat quenching factor is Q ′ = 0.91 ± 0.03 ± 0.04 , where the two errors are the contributions from the Q and Q / Q ′ measurements, respectively. The present compilation of Q values and evaluation of Q ′ represent one of the most precise determinations of the absolute energy scale for any detector used in direct searches for WIMP dark matter.

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.

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.