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.