The CRESST-II experiment uses cryogenic detectors to search for nuclear recoil events induced by the elastic scattering of dark matter particles in CaWO 4 crystals. Given the low energy threshold of our detectors in combination with light target nuclei, low mass dark matter particles can be probed with high sensitivity. In this letter we present the results from data of a single detector module corresponding to 52 kg live days. A blind analysis is carried out. With an energy threshold for nuclear recoils of 307 eV we substantially enhance the sensitivity for light dark matter. Thereby, we extend the reach of direct dark matter experiments to the sub-GeV/c 2 region and demonstrate that the energy threshold is the key parameter in the search for low mass dark matter particles.

Models for light dark matter particles with masses below 1 GeV/c 2 are a natural and well-motivated alternative to so-far unobserved weakly interacting massive particles. Gram-scale cryogenic calorimeters provide the required detector performance to detect these particles and extend the direct dark matter search program of CRESST. A prototype 0.5 g sapphire detector developed for the ν-cleus experiment has achieved an energy threshold of E th = (19.7 ± 0.9) eV. This is one order of magnitude lower than for previous devices and independent of the type of particle interaction. The result presented here is obtained in a setup above ground without significant shielding against ambient and cosmogenic radiation. Although operated in a highbackground environment, the detector probes a new range of light-mass dark matter particles previously not accessia Associated with the CRESST collaboration for this work.

The CRESST-II cryogenic dark matter search aims for the detection of WIMPs via elastic scattering off nuclei in CaWO 4 crystals. We present results from a lowthreshold analysis of a single upgraded detector module. This module efficiently vetoes low energy backgrounds induced by α-decays on inner surfaces of the detector. With an exposure of 29.35 kg live days collected in 2013 we set a limit on spin-independent WIMP-nucleon scattering which probes a new region of parameter space for WIMP masses below 3 GeV/c 2 , previously not covered in direct detection searches. A possible excess over background discussed for the previous CRESST-II phase 1 (from 2009 to 2011) is not confirmed.

The cryogenic dark matter experiment CRESST-II aims at the direct detection of WIMPs via elastic scattering off nuclei in scintillating CaWO 4 crystals. We present a new, highly improved, detector design installed in the current run of CRESST-II Phase 2 with an efficient active rejection of surface-alpha backgrounds. Using CaWO 4 sticks instead of metal clamps to hold the target crystal, a detector housing with fully-scintillating inner surface could be realized. The presented detector (TUM40) provides an excellent threshold of ∼0.60 keV and a resolution of σ ≈ 0.090 keV (at 2.60 keV). With significantly reduced background levels, TUM40 sets stringent limits on the spin-independent WIMPnucleon scattering cross section and probes a new region of parameter space for WIMP masses below 3 GeV/c 2 . In this paper, we discuss the novel detector design and the surfacealpha event rejection in detail.

Scintillating CaWO 4 single crystals are a promising multi-element target for rare-event searches and are currently used in the direct dark matter experiment CRESST (Cryogenic Rare Event Search with Superconducting Thermometers). The relative light output of different particle interactions in CaWO 4 is quantified by quenching factors (QFs). These are essential for an active background discrimination and the identification of a possible signal induced by weakly interacting massive particles (WIMPs). We present the first precise measurements of the QFs of O, Ca and W at mK temperatures by irradiating a cryogenic detector with a fast neutron beam. A clear energy dependence of the QF of O and, less pronounced, of Ca was observed for the first time. Furthermore, in CRESST neutron-calibration data a variation of the QFs among different CaWO 4 single crystals was found. For typical CRESST detectors the QFs in the region-of-interest (10-40 keV) are QF ROI O = (11.2 ± 0.5) %, QF ROI Ca = (5.94±0.49) % and QF ROI W = (1.72±0.21) %. The latest CRESST data (run32) is reanalyzed using these fundamentally new results on light quenching in CaWO 4 having moderate influence on the WIMP analysis. Their relevance for future CRESST runs and for the clarification of previa