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Register a new userCombined Limits on WIMPs from the CDMS and EDELWEISS Experiments
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Added by
Philippe Di Stefano
Publication date
2011
fields
Physics
and research's language is
English
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The CDMS and EDELWEISS collaborations have combined the results of their direct searches for dark matter using cryogenic germanium detectors. The total data set represents 614 kg.d equivalent exposure. A straightforward method of combination was chosen for its simplicity before data were exchanged between experiments. The results are interpreted in terms of limits on spin-independent WIMP-nucleon cross-section. For a WIMP mass of 90 GeV/c^2, where this analysis is most sensitive, a cross-section of 3.3 x 10^{-44} cm^2 is excluded at 90% CL. At higher WIMP masses, the combination improves the individual limits, by a factor 1.6 above 700 GeV/c^2. Alternative methods of combining the data provide stronger constraints for some ranges of WIMP masses and weaker constraints for others.
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We present the results of a search for elastic scattering from galactic dark matter in the form of Weakly Interacting Massive Particles (WIMPs) in the 4-30 GeV/$c^2$ mass range. We make use of a 582 kg-day fiducial exposure from an array of 800 g Germanium bolometers equipped with a set of interleaved electrodes with full surface coverage. We searched specifically for $sim 2.5-20$ keV nuclear recoils inside the detector fiducial volume. As an illustration the number of observed events in the search for 5 (resp. 20) GeV/$c^2$ WIMPs are 9 (resp. 4), compared to an expected background of 6.1 (resp. 1.4). A 90% CL limit of $4.3times 10^{-40}$ cm$^2$ (resp. $9.4times 10^{-44}$ cm$^2$) is set on the spin-independent WIMP-nucleon scattering cross-section for 5 (resp. 20) GeV/$c^2$ WIMPs. This result represents a 41-fold improvement with respect to the previous EDELWEISS-II low-mass WIMP search for 7 GeV/$c^2$ WIMPs. The derived constraint is in tension with hints of WIMP signals from some recent experiments, thus confirming results obtained with different detection techniques.
We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range $m_chi in [4, 30],mathrm{GeV}/c^2$ with the EDELWEISS-III experiment. A 2D profile likelihood analysis is performed on data from eight selected detectors with the lowest energy thresholds leading to a combined fiducial exposure of 496 kg-days. External backgrounds from $gamma$- and $beta$-radiation, recoils from $^{206}$Pb and neutrons as well as detector intrinsic backgrounds were modelled from data outside the region of interest and constrained in the analysis. The basic data selection and most of the background models are the same as those used in a previously published analysis based on Boosted Decision Trees (BDT). For the likelihood approach applied in the analysis presented here, a larger signal efficiency and a subtraction of the expected background lead to a higher sensitivity, especially for the lowest WIMP masses probed. No statistically significant signal was found and upper limits on the spin-independent WIMP-nucleon scattering cross section can be set with a hypothesis test based on the profile likelihood test statistics. The 90% C.L. exclusion limit set for WIMPs with $m_chi = 4,mathrm{GeV/}c^2$ is $1.6 times 10^{-39},mathrm{cm^2}$, which is an improvement of a factor of seven with respect to the BDT-based analysis. For WIMP masses above $15,mathrm{GeV/}c^2$ the exclusion limits found with both analyses are in good agreement.
Bosonic super-WIMPs, including pseudoscalar and vector particles, are dark matter candidates. Until now, many underground experiments searches for super-WIMPs have been performed in the mass range of a few $rm keV/c^2$ to 1 $rm MeV/c^2$. All these searches utilize the absorption process of a super-WIMP by a target atom in the detector, which is similar to the photoelectric effect. In this study, we consider another process, namely, a Compton-like process. As an example, we compare the cross-section of a germanium atom for the absorption process with that of a Compton-like process. Our findings indicate that the cross-section for the Compton-like process becomes dominant, compared to that for the absorption process for mass above approximately 150 $rm keV/c^2$ for both pseudoscalar and vector super-WIMPs. In particular, the cross-section for the Compton-like process for a vector super-WIMP becomes increasingly greater than that for the absorption process by an order of magnitude to two orders of magnitude in the 400 $rm keV/c^2$ to 1 $rm MeV/c^2$ mass range, respectively. By including the Compton-like process, which has not been used in any other super-WIMP search experiment, the experimental upper limits can be improved.
We investigate the impact of prior models on the upper bound of the sum of neutrino masses, $sum m_{ u}$. We use data from Large Scale Structure of galaxies, Cosmic Microwave Background, Type Ia SuperNovae, and Big Bang Nucleosynthesis. We probe physically motivated neutrino mass models (respecting oscillation experiment constraints) and compare them to constraints using standard cosmological approximations. The former give a consistent upper bound of $sum m_{ u} lesssim 0.26$ eV ($95%$ CI) and yields a strong competitive upper bound for the lightest neutrino mass species, $m_0^{ u} < 0.086$ eV ($95%$ CI). By contrast one of the approximations, which is somewhat inconsistent with oscillation experiments, yields an upper bound of $sum m_{ u} lesssim 0.15$ eV ($95%$ CI), which differs substantially from the former upper bound. We, therefore, argue that cosmological neutrino mass and hierarchy determination should be pursued using physically motivated models since approximations might lead to incorrect and nonphysical upper bounds.
We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below ~10 GeV/c^2. This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c^2 and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments.
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