Pulse shape discrimination and dark matter search with NaI (Tl) scintillator at Laboratoire Souterrain de Modane

Underground data for WIMP search have been obtained from a 83 days run in a low activity environment at the Laboratoire Souterrain de Modane (LSM), wi th a 10 kg NaI(Tl) detector. The obtained high photoelectron yield allowed an energy threshold of 2 keV. A low energy peak in the energy spectrum limi ts the sensitivity to Spin Independent coupling WIMP investigation. Pulse s hape analysis of the data have shown an unexpected population of events, al so observed by another experiment at the same rate. A possible interpretati on of these events is related to alpha decays of radon isotope at the surfa ce of the crystal.