Measurement of nuclear recoil quenching factors in CaWO4

The CRESST experiment, aiming at the direct detection of WIMPs via nuclear recoils, is currently using scintillating CaWO4 crystals. The WIMP–nucleus cross section for elastic scattering as well as the scintillation efficiency differ considerably for recoils from Ca, W and O in these crystals. Therefore a discriminating detector calibration is essential in order to improve WIMP parameter claims. At the tandem accelerator of the Maier-Leibnitz-Laboratory (MLL) in Garching, Germany, a neutron scattering facility is operated for the determination of the individual quenching factors (QF) in the bulk of a CaWO4 crystal to better understand the detector response to neutron background and a possible WIMP signal. First measurements at room temperature reveal QF(O) = 7.8 ± 0.3% (recoil energy 1.0–2.2 MeV), QF(Ca) = 6.3 ± 1.6% (recoil energy 0.4–1 MeV), QF(W) < 3.0% (2σ, recoil energy 0.1 MeV).