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Register a new userPerformance of the EDELWEISS-III experiment for direct dark matter searches
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We present the results of measurements demonstrating the efficiency of the EDELWEISS-III array of cryogenic germanium detectors for direct dark matter searches. The experimental setup and the FID (Fully Inter-Digitized) detector array is described, as well as the efficiency of the double measurement of heat and ionization signals in background rejection. For the whole set of 24 FID detectors used for coincidence studies, the baseline resolutions for the fiducial ionization energy are mainly below 0.7 keV$_{ee}$ (FHWM) whereas the baseline resolutions for heat energies are mainly below 1.5 keV$_{ee}$ (FWHM). The response to nuclear recoils as well as the very good discrimination capability of the FID design has been measured with an AmBe source. The surface $beta$- and $alpha$-decay rejection power of $R_{rm surf} < 4 times 10^{-5}$ per $alpha$ at 90% C.L. has been determined with a $^{210}$Pb source, the rejection of bulk $gamma$-ray events has been demonstrated using $gamma$-calibrations with $^{133}$Ba sources leading to a value of $R_{gamma{rm -mis-fid}} < 2.5 times 10^{-6}$ at 90% C.L.. The current levels of natural radioactivity measured in the detector array are shown as the rate of single $gamma$ background. The fiducial volume fraction of the FID detectors has been measured to a weighted average value of $(74.6 pm 0.4)%$ using the cosmogenic activation of the $^{65}$Zn and $^{68,71}$Ge isotopes. The stability and uniformity of the detector response is also discussed. The achieved resolutions, thresholds and background levels of the upgraded EDELWEISS-III detectors in their setup are thus well suited to the direct search of WIMP dark matter over a large mass range.
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The DAMIC experiment uses fully depleted, high resistivity CCDs to search for dark matter particles. With an energy threshold $sim$50 eV$_{ee}$, and excellent energy and spatial resolutions, the DAMIC CCDs are well-suited to identify and suppress radioactive backgrounds, having an unrivaled sensitivity to WIMPs with masses $<$6 GeV/$c^2$. Early results motivated the construction of a 100 g detector, DAMIC100, currently being installed at SNOLAB. This contribution discusses the installation progress, new calibration efforts near the threshold, a preliminary result with 2014 data, and the prospects for physics results after one year of data taking.
A variety of detectors has been proposed for dark matter direct detection, but most of them -- by the fact -- are still at R&D stage. In many cases, it is claimed that the lack of an adequate detectors radio-purity might be compensated through heavy uses of MonteCarlo simulations, subtractions and handlings of the measured counting rates, in order to claim higher sensitivity (just for a particular scenario). The relevance of a correct evaluation of systematic effects in the use of MonteCarlo simulations at very low energy (which has always been safely discouraged in the field so far) and of multiple subtractions and handling procedures applied to the measured counting rate is shortly addressed here at some extent. Many other aspects would also deserve suitably deep investigations.
In the past decades, several detector technologies have been developed with the quest to directly detect dark matter interactions and to test one of the most important unsolved questions in modern physics. The sensitivity of these experiments has improved with a tremendous speed due to a constant development of the detectors and analysis methods, proving uniquely suited devices to solve the dark matter puzzle, as all other discovery strategies can only indirectly infer its existence. Despite the overwhelming evidence for dark matter from cosmological indications at small and large scales, a clear evidence for a particle explaining these observations remains absent. This review summarises the status of direct dark matter searches, focussing on the detector technologies used to directly detect a dark matter particle producing recoil energies in the keV energy scale. The phenomenological signal expectations, main background sources, statistical treatment of data and calibration strategies are discussed.
We present measurements of the electron-recoil (ER) response of the LUX dark matter detector based upon 170,000 highly pure and spatially-uniform tritium decays. We reconstruct the tritium energy spectrum using the combined energy model and find good agreement with expectations. We report the average charge and light yields of ER events in liquid xenon at 180 V/cm and 105 V/cm and compare the results to the NEST model. We also measure the mean charge recombination fraction and its fluctuations, and we investigate the location and width of the LUX ER band. These results provide input to a re-analysis of the LUX Run3 WIMP search.
The direct search for dark matter is entering a period of increased sensitivity to the hypothetical Weakly Interacting Massive Particle (WIMP). One such technology that is being examined is a scintillation only noble liquid experiment, MiniCLEAN. MiniCLEAN utilizes over 500 kg of liquid cryogen to detect nuclear recoils from WIMP dark matter and serves as a demonstration for a future detector of order 50 to 100 tonnes. The liquid cryogen is interchangeable between argon and neon to study the A$^{2}$ dependence of the potential signal and examine backgrounds. MiniCLEAN utilizes a unique modular design with spherical geometry to maximize the light yield using cold photomultiplier tubes in a single-phase detector. Pulse shape discrimination techniques are used to separate nuclear recoil signals from electron recoil backgrounds. MiniCLEAN will be spiked with additional $^{39}$Ar to demonstrate the effective reach of the pulse shape discrimination capability. Assembly of the experiment is underway at SNOLAB and an update on the project is given.
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