Study of remaining electrons in XENON100

Several gravitational phenomena suggest the presence of non-luminous matter, named dark matter, which is responsible for about a quarter of the total energetic budget of the Universe. One of the most compelling candidates to describe it are WIMPs (Weakly Interactive Massive Particles). In order to directly detect these particles, the XENON Collaboration has conceived and built dual phase (liquid/gas) time projection chambers (TPC) filled with xenon, among which the XENON100 detector. When a particle interacts with the detector target, it excites and ionizes xenon atoms. Photons from the atoms deexcitation generate a scintillation signal known as S1. The electrons from the ionization follow the applied electric field lines and drift towards the gas phase where they interact to generate a second signal, called S2. During long periods of data taking it is important to keep the detector operational and to continuously monitor its performance. Single electrons represent an ideal probe to achieve this goal as they do not need dedicated calibration time. These electrons produce small charge signals consisting of single to a few electrons in accidental coincidences. They are induced by the photoelectric effect of S1 and S2 photons on either xenon impurities or on the TPC detector's materials. The use of single electrons thus allows to properly control the detector stability. They can also be used to probe the presence of the residual electrons background present in the detector. (author)