Search

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present Four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO4 and simultaneous measurement of phonons and scintillation light is in preparation. (C) 2000 Elsevier Science B.V. All rights reserved.

Results of the CRESST experiment at Gran Sasso using 262-g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the Galactic halo. The sapphire defectors are especially sensitive to low-mass WIMPs with spin-dependent interaction and improve on existing limits in this region. (C) 2003 MAIK "Nauka/Interperiodica".

International audience; To investigate fractoluminescence in scintillating crystals used for particle detection, we have developed a multi-channel setup built around samples of double-cleavage drilled compression (DCDC) geometry in a controllable atmosphere. The setup allows the continuous digitization over hours of various parameters, including the applied load, and the compressive strain of the sample, as well as the acoustic emission. Emitted visible light is recorded with nanosecond resolution, and crack propagation is monitored using infrared lighting and camera. An example of application to $\text{B}{{\text{i}}_{4}}\text{G}{{\text{e}}_{3}}{{\text{O}}_{12}}$ (BGO) is provided.

In prospect of its application in cryogenic rare-event searches, we have investigated the low-temperature scintillation properties of CaWO4 crystals down to 3.4 K under {\alpha} and {\gamma} excitation. Concerning the scintillation decay times, we observe a long component in the ms range which significantly contributes to the light yield below 40K. For the first time we have measured the temperature dependence of the {\alpha}/{\gamma}- ratio of the light yield. This parameter which can be used to discriminate {\alpha} and {\gamma} events in scintillating bolometers is found to be about 8-15% smaller at low temperatures compared to room temperature., Comment: The following article has been accepted by Journal of Applied Physics. After it is published, it will be found at http://scitation.aip.org/content/aip/journal/jap

We report on simultaneous detection of phonons and scintillation light using a cryogenic calorimeter composed of a scintillating CaWO 4 crystal and a separate light detector, both instrumented with a tungsten superconducting phase transition thermometer operating at about 12 mK. Clear discrimination between electron and nuclear recoils was demonstrated by irradiating the detector with electrons, photons and neutrons. The shape of the nuclear recoil energy spectrum induced by the neutrons could be well reproduced by simulations.

The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors. Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events. Surface event rejection capabilities were tested with two [superscript 210] Pb sources producing ∼130 beta decays/hr. In ∼800 live hours, no events leaked into the 8–115 keV signal region, giving upper limit leakage fraction 1.7 × 10[superscript −5] at 90% C.L., corresponding to, United States. Dept. of Energy (Contract No. DE-AC03-76SF00098), United States. Dept. of Energy (Contract No. DE-FG02-92ER40701), United States. Dept. of Energy (Contract No. DE-FG02-94ER40823), United States. Dept. of Energy (Contract No. DE-FG03-90ER40569), United States. Dept. of Energy (Contract No. DE-FG03-91ER40618), United States. Dept. of Energy (Contract No. DE-SC0004022), National Science Foundation (U.S.) (Grant No. AST-9978911), National Science Foundation (U.S.) (Grant No. NSF-0847342), National Science Foundation (U.S.) (Grant No. PHY-1102795), National Science Foundation (U.S.) (Grant No. NSF-1151869), National Science Foundation (U.S.) (Grant No. PHY-0542066), National Science Foundation (U.S.) (Grant No. PHY-0503729), National Science Foundation (U.S.) (Grant No. PHY-0503629), National Science Foundation (U.S.) (Grant No. PHY-0503641), National Science Foundation (U.S.) (Grant No. PHY-0504224), National Science Foundation (U.S.) (Grant No. PHY-0705052), National Science Foundation (U.S.) (Grant No. PHY-0801708), National Science Foundation (U.S.) (Grant No. PHY-0801712), National Science Foundation (U.S.) (Grant No. PHY-0802575), National Science Foundation (U.S.) (Grant No. PHY-0847342), National Science Foundation (U.S.) (Grant No. PHY-0855299), National Science Foundation (U.S.) (Grant No. PHY-0855525), National Science Foundation (U.S.) (Grant No. PHY-1205898)

Results are presented from a reanalysis of the entire five-tower data set acquired with the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory, with an exposure of 969 kg-days. The analysis window was extended to a recoil energy of 150 keV, and an improved surface-event background-rejection cut was defined to increase the sensitivity of the experiment to the inelastic dark matter (iDM) model. Three dark matter candidates were found between 25 keV and 150 keV. The probability to observe three or more background events in this energy range is 11%. Because of the occurrence of these events the constraints on the iDM parameter space are slightly less stringent than those from our previous analysis, which used an energy window of 10-100 keV., 10 pages, 10 figures, minor changes to match published version, conclusion unchanged

A method to stabilize cryogenic detectors with superconducting phase transition thermometers in their operating point is presented. Measurements of X-ray lines emitted by an 55 Fe X-ray fluorescence source showed an improvement in energy resolution from 230 to 133 eV on the 1.5 keV aluminium line with this technique. Furthermore the required set-up allows to simulate real events by injecting heat pulses into the thermometer and in this way to calibrate the detector and to monitor its long-term stability.

Diffusion of quasiparticles over distances up to 4 mm has been observed in various superconducting films. The quasiparticles were created by X-ray absorption in film strips with critical temperatures near 1 K and were detected in two superconducting phase transition thermometers at the ends of each strip. Position and energy of the absorbed X-rays as well as diffusion constants and lifetimes of the quasiparticles were determined. Very long lifetimes up to 9 ms allow the realization of large area phonon collector films on massive cryogenic particle detectors. Recently, with a first such detector a high efficiency of the phonon collection could be demonstrated.

In the early stages of running of the CRESST dark matter search using sapphire detectors at very low temperature, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time the energy release in fracture has been directly and accurately measured on a microscopic event-by-event basis. The energy threshold corresponds to the breaking of only a few hundred covalent bonds, a sensitivity some orders of magnitude greater than that of previous technique. We report some features of the data, including energy distributions, waiting time distributions, autocorrelations and the Hurst exponent. The energy distribution appear to follow a power law, $dN/dE\propto E^{-\beta}$, similar to the power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain,the waiting time $w$ or gap distribution between events has a power law behavior at small $w$ and an exponential fall-off at large $w,$ and can be fit $\propto w^{-\alpha}e^{-w/w_0}$. The autocorrelation function shows time correlations lasting for substantial parts of an hour. An asymmetry is found around large events, with higher count rates after, as opposed to before,the large event ., Comment: Fig 4 and surrounding discussion changed. References added, langauge clarified, with greater stress on sensitivity and total energy detection. Error in metadata fixed

In the early stages of running of the CRESST dark matter search with sapphire crystals as detectors, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time that the energy release in fracture has been accurately measured on a microscopic event-by-event basis. The energy distributions appear to follow a power law, dN/dE proportional to E-beta, similar to the Gutenberg-Richter power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain, the autocorrelation function shows time correlations lasting for substantial parts of an hour. Some remarks are made concerning the possible role Of Such mechanical stress release processes in the noise of sensitive cryodetectors. (c) 2006 Elsevier B.V. All rights reserved.

We apply the standard photovoltaic technique of texturing to reduce the reflectivity of silicon cryogenic calorimetric light detectors. In the case of photons with random incidence angles, absorption is compatible with the increase in surface area. For the geometrically thin detectors studied, energy resolution from athermal phonons, dominated by position dependence, is proportional to the surface-to-volume ratio. With the CaWO4 scintillating crystal used as light source, the time constants of the calorimeter should be adapted to the relatively slow light-emission times., Submitted to Journal of Applied Physics

Results of the CRESST experiment at Gran Sasso using 262 g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the galactic halo. The sapphire detectors are especially sensitive for low-mass WIMPS with spin-dependent interaction and improve on existing limits in this region.