Hans Kraus

Abstract:

For the first time the natural alpha decay of W-180 has been unambiguously detected in a (gamma, beta and neutron)-free background spectrum. This has been obtained by simultaneously measuring phonon and light signals with CRESST 11 cryogenic detectors. Results on the radio purity of the detectors and on the measured half-life of W-180 are presented.

Abstract:

The mass number dependence of the WIMP-nucleus scattering offers a method for identifying a true WIMP signal over a neutron background. In this paper we present a study on using a combination of ZnWO4 and CaWO4 absorbers to exploit this materials signature for WIMP detection. We show that already modest exposure in the region of 5 kg years should allow the detection of WIMP interaction for cross sections smaller than current experimental sensitivities. The combination of these two tungstates could form the basis of the first multi-target detector capable of WIMP identification through materials signature.

Abstract:

We present first competitive results on WIMP dark matter using the phonon-light-detection technique. A particularly strong limit for WIMPs with coherent scattering results from selecting a region of the phonon-light plane corresponding to tungsten recoils. The observed count rate in the neutron band is compatible with the rate expected from neutron background. CRESST is presently being upgraded with a 66 channel SQUID readout system, a neutron shield and a muon veto system. This results in a significant improvement in sensitivity.

Abstract:

Thermodynamic properties of CaWO4 were studied using the GULP code incorporating semiclassical simulations based on quasiharmonic lattice dynamics and static lattice minimisation methods. Free energy minimization along with so called "relax" fitting was used to obtain the parameters characterising the interatomic interaction potential. From analyses of the calculated and experimental cell sizes, thermal expansion coefficients, elastic constants, phonon density of states, heat capacity, entropy, and Grüneisen parameters it is concluded that quasiharmonic lattice dynamics give a good description of these properties of CaWO4 at temperatures up to 800 K.