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Register a new userImproved Exclusion Limits from the EDELWEISS WIMP Search
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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 10 TeV/c2, 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 of 7.4 kg.days. 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%CL a WIMP candidate with a mass of 44 GeV/c2 and a cross-section of 5.4 x 10-6 pb, as reported by the DAMA collaboration. A first sample of supersymmetric models are also excluded at 90%CL.
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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(10-20 mu-m 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.
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.
Bubble Chambers provided the dominant particle detection technology in accelerator experiments for several decades, eventually falling into disuse with the advent of other techniques. We report here on the first period of operation of an ultra-clean, room-temperature bubble chamber containing 1.5 kg of superheated CF$_{3}$I, a target maximally sensitive to spin-dependent and -independent Weakly Interacting Massive Particle (WIMP) couplings. An exposure in excess of 250 kg-days is obtained, with a live-time fraction reaching 80%. This illustrates the ability to employ bubble chambers in a new realm, the search for dark matter particles. Improved limits on the spin-dependent WIMP-proton scattering cross section are extracted from this first period. An extreme intrinsic insensitivity to the backgrounds commonly limiting these experiments (a rejection factor for photon-induced electrons of $sim10^{-10}$) has been measured in operating conditions leading to the detection of low-energy nuclear recoils such as those expected from WIMPs.
The SIMPLE project uses superheated C2ClF5 liquid detectors to search for particle dark matter candidates. We report the results of the first stage exposure (14.1 kgd) of its latest two-stage, Phase II run, with 15 superheated droplet detectors of total active mass 0.208 kg. In combination with the results of the neutron-spin sensitive XENON10 experiment, these results yield a limit of |a_p| < 0.32, |a_n| < 0.17 for M_W = 50 GeV/c2 on the model-independent, spin-dependent sector of weakly interacting massive particle (WIMP)-nucleus interactions, and together yield a 50% reduction in the previously allowed region of the phase space. The result provides a contour minimum of {sigma}_p ~ 2.8 x 10-2 pb at M_W = 45 GeV/c2, constituting the most restrictive direct detection limit to date against a spin-dependent WIMP-proton coupling. In the spin-independent sector, the result is seen to offer the prospect of contributing to the question of light mass WIMPs with an improvement in the current understanding of its nucleation efficiency.
The EDELWEISS-II experiment uses cryogenic heat-and-ionization detectors in order to detect the rare interactions from possible WIMP dark matter particles on Germanium nuclei. Recently, new-generation detectors with an interleaved electrode geometry were developped and validated, enabling an outstanding rejection of gamma-rays and surface interactions. We present here preliminary results of a one-year WIMP search carried out with ten of such detectors in the Laboratoire Souterrain de Modane. A sensitivity to the spin-independent WIMP-nucleon cross-section of 5 times 10-8 pb was achieved using a 322 kg
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