  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-region and demonstrate
that the energy threshold is the key parameter in the search for low mass dark
matter particles.
