Characterization of the Response of CaWO4 on Recoiling Nuclei from Surface Alpha Decays

Abstract

A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from 210Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration measurements have been performed at the TU Munchen. A for this purpose an optimized version of the CRESST detector has been developed consisting of a 38 g CaWO4 crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous measurement of the phonon signal and the scintillation light from the CaWO4 crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results of a first measurement with a 210Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.