The dark matter search experiment CRESST-II (Cryogenic Rare Event Search with Super- conducting Thermometers) aims at the direct detection of WIMPs (Weakly Interacting Massive Particles) which are candidates to account for the non-baryonic Dark Matter content in our universe. The CRESST-II detector uses cryogenic phonon-light detector- modules with CaWO4 as target material to achieve the required event-by-event background suppression for the rare event search. The efficiency of this background-suppression tech- nique is based on the performance of the light detector as well as on the knowledge and understanding of the differing light-quenching effect observed for different interacting par- ticles in CaWO4.
In my talk, I will first address different possibilities that were investigated in order to improve and understand the background-suppression capability of CRESST detector mo- dules. Experimental results obtained with a cryogenic light detector built according to the so-called composite detector design as well as with a Neganov-Luke amplified light detector are presented. The potential of these two techniques to optimize the background- suppression capability of CRESST detector modules is discussed.
In the second part of my talk, a comprehensive microscopic model developed to explain the light generation and the light-quenching effect observed for different interacting particles in CaWO4 will be presented. This model not only predicts the different amounts of scin- tillation light generated for different interacting particles, but also allows to calculate the decay-time spectrum of the scintillation light. Thus, it has been possible to determine the free model parameters and to validate the model independently of the produced amount of scintillation light. With this model, quenching factors for different particle energies and for different temperatures and defect concentrations of the CaWO4 crystal were calculated. The results will be described.
