Direct dark matter search with the CRESST II detector

CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) is an experiment aimed at the direct detection of Dark Matter. The experiment uses scintillating CaWO4 single crystals operated at mK-temperatures to measure the recoil energy deposited by elastic WIMP (Weakly Interacting Massive Particle) nucleon scattering. By recording phonons as well as the associated scintillation light generated by an energy deposition in the crystal, CRESST is able to achieve a unique background suppression on an event-by-event level. In a two-year measuring campaign CRESST II has gathered ∝730 kg days of data. In the analyzed data set an excess of events in the region of interest was observed and is at present difficult to explain with contributions from common backgrounds such as alpha-, beta-, gamma-radiation or neutrons. In a maximum likelihood analysis it could be demonstrated that these backgrounds alone are not sufficient to account for the number of events observed. However, the addition of a signal induced by a relatively light WIMP (10-30 GeV) could explain the observed discrepancy on a ≥4.2σ level. The associated parameters for such a Dark Matter particle are discussed. The talk concludes with an outlook on future efforts to pin down the nature of the observed events and on the low-temperature detector developments required to further reduce background.