Dark Matter Results from 225 Live Days of XENON100 Data

We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso for 13 months during 2011 and 2012. XENON100 features an ultralow electromagnetic background of (5.3±0.6)×10-3  events/(keVee×kg×day) in the energy region of interest. A blind analysis of 224.6 live days×34  kg exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the predefined nuclear recoil energy range of 6.6–30.5  keVnr are consistent with the background expectation of (1.0±0.2) events. A profile likelihood analysis using a 6.6–43.3  keVnr energy range sets the most stringent limit on the spin-independent elastic weakly interacting massive particle–nucleon scattering cross section for weakly interacting massive particle masses above 8  GeV/c2, with a minimum of 2×10-45  cm2 at 55  GeV/c2 and 90% confidence level.