Hans Kraus

Abstract:

Following the investigations of the structure and scintillation properties of Ca-doped zinc tungstate powder [phys. stat. sol. (a) 204. 730 (2007)] a single-crystal of ZnWO4-Ca (0.5 mol%) was grown and characterised. The relative light output, energy resolution and decay characteristics were measured for pure and Ca-doped ZnWO4 scintillators. An increase in the light yield of ~40% compared with the undoped crystal, and an energy resolution 9.6% (137Cs) were obtained for Ca-doped ZnWO4. The observed improvement is attributed to the reduction of self-absorption (bleaching) of the crystal. The cause of bleaching as well as the possible contribution of scattering is discussed. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

Abstract:

European Underground Rare Event Calorimeter Array (EURECA) will be an astro-particle physics facility in the Laboratoire Souterrain de Modane, aiming to directly detect galactic dark matter. The EURECA collaboration unites CRESST, EDELWEISS and the Spanish-French experiment ROSEBUD, thus concentrating and focussing effort on cryogenic detector research in Europe into a single facility. The aim is to explore WIMP - nucleon scalar cross sections in the 10 - 10 picobarn region with a target mass of up to one ton. A major advantage of EURECA is the planned use of more than just one target material (multi target experiment for WIMP identification).

Abstract:

The perspective of using CaMoO4 as a scintillation target in cryogenic rare event searches has provided strong motivation for the optimisation of this material. A single crystal of CaMoO4, exhibiting high optical quality, was produced and its scintillation light response to particle excitation and its decay time constant were investigated over the 7-300K temperature range. The scintillation at room temperature is strongly affected by thermal quenching. The main decay time constant is found to be 15.7 +/- 0.4 mu s at T= 300K; cooling to 7K increases the scintillation decay time constant to 380 +/- 20 mu s. The scintillation efficiency of the CaMoO4 crystal was evaluated by comparison with a reference CaWO4 crystal measured under the same conditions; we estimate the light output of CaMoO4 to be 55 +/- 20% that of CaWO4 at 294K and 95 +/- 30% at 7K. The study confirmed that calcium molybdate optimised for high light yield is a very attractive material for use in cryogenic phonon-scintillation detectors in rare event searches. (c) 2007 Elsevier B.V. All rights reserved.

Abstract:

CRESST I1 is a WIMP search experiment using cryogenic detectors to detect heat and scintillation signals in Caw04 crystals simultaneously. Competitive limits on the coherent WIMP-nucleon scattering cross section and other results from runs from the upgrade to CRESST I1 are shown. New features and upgrades installed on the CRESST I1 setup are described and the status of the experiment is presented.

Abstract:

We present results on WIMP dark matter interaction, obtained using cryogenic phonon-scintillation detectors. The targets are CaWO4 scintillating crystals with phonon sensors, while scintillation is detected with an associated cryogenic light detector. The combination of phonon and light signals leads to a strong suppression of nonnuclear recoil backgrounds. Results obtained before the upgrade of CRESST are presented and a status report on the upgrade itself is given.