In situ determination of quenching factors in CRESST-II

The CRESST-II experiment is searching for WIMPs (Weakly Interacting Massive Particles) via their elastic scattering off nuclei in scintillating CaWO4 single crystals at low temperatures. Each particle interaction in CaWO4 produces a phonon as well as a light signal. The ratio between the recorded light and phonon signal - the Quenching Factor (QF) - is a crucial parameter to discriminate very efficiently between electron recoils from radioactive e/γ background and nuclear recoils, e.g. WIMP events. Moreover, to some extent, the different types of recoiling nuclei (O, Ca, W) can be distinguished, if the QF's are known accurately enough. The QF cannot only be extracted from dedicated experiments but also from calibration data, gathered with an AmBe-source placed inside and outside the neutron shielding of CRESST-II. In this talk we present a method to determine the QFs of CaWO4 in situ from these calibration data. Furthermore, first results will be shown, discussed and compared to other measurements.