Study of the electromagnetic background in the XENON100 experiment

xenon nuclei. We present a comprehensive study of the predicted electronic recoil background coming from radioactive decays inside the detector and shield materials, and intrinsic radioactivity in the liquid xenon. Based on GEANT4 Monte Carlo simulations using a detailed geometry together with the measured radioactivity of all detector components, we predict an electronic recoil background in the WIMP-search energy range and 30 kg ducial mass of less than 10 2 events kg 1 day 1 keV 1 , consistent with the experiment’s design goal. The predicted background spectrum is in very good agreement with the data taken during the commissioning of the detector in Fall 2009.