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Abstract:

In this paper we present a characterisation of ZnMoO4 using spectroscopic techniques. Reflection, luminescence and luminescence excitation spectra were measured over the temperature range 8-295 K using VUV synchrotron radiation. The emission spectrum of the crystal exhibits a broad band with a maximum around 1.95 eV at 80 K that is attributed to the radiative transitions within MO4^2- oxyanion complex. An interpretation of the observed features of the electronic excitations in the crystal is given based on present knowledge of the electronic structure and emission properties of molybdate crystals. The results of this study suggest that ZnMoO4 is a suitable candidate for further testing for implementation as a target material in cryogenic scintillation searches for rare events. © 2006 Elsevier B.V. All rights reserved.

Abstract:

The CRESST experiment is looking for non-baryonic particle dark matter via nuclear scattering in CaWO4. The simultaneous measurement of the heat and the scintillation light generated by an event in a CaWO4 single crystal is used to discriminate between electron and nuclear recoils thanks to their different light output. This allows an efficient suppression of the electron recoil background. The set-up consists of modules with a 300 g CaWO4 crystal mounted in a reflective housing together with a light detector. The heat signal is read out using a superconducting transition-edge sensor (TES) made of tungsten evaporated directly onto the crystal that is operated at a few mK. Currently the second phase of the experiment is being set up at the Laboratori Nazionali del Gran Sasso in which it is planned to run 33 detector modules providing a total target mass of 10 kg. First test runs with prototype detectors have been successfully performed.

Abstract:

We present first significant limits on WIMP dark matter by the phonon-light technique, where combined phonon and light signals from a scintillating cryogenic detector are used to suppress the non-nuclear recoil background. The performance of the detectors developed for the second phase of the CRESST experiment will be discussed and data collected with two prototype modules in a short run, corresponding to a net exposure of 20.5 kg days, will be presented. (c) 2005 Elsevier B.V. All rights reserved.

Abstract:

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.

Abstract:

We have developed multichannel SQUID systems for two particle physics experiments: a 66-channel system for detector readout in the CRESST dark matter search, and a 12-channel magnetometry system for the CryoEDM neutron electric dipole moment experiment. These different applications have different requirements, for example in the CRESST system it is important to minimise crosstalk, while the CryoEDM system must be shielded from magnetic noise. Future experiments such as the EURECA dark matter project may require systems with a much higher number of channels. (c) 2006 Elsevier B.V. All rights reserved.