Event categories in the EDELWEISS WIMP search experiment

Four categories of events have been identified in the EDELWEISS-I dark matt er experiment using germanium cryogenic detectors measuring simultaneously charge and heat signals. These categories of events are interpreted as elec tron and nuclear interactions occurring in the volume of the detector. and electron and nuclear interactions occurring close to the surface of the det ectors (within approximate to 10-20 mu m of the surface). We discuss the hy pothesis that low energy surface nuclear recoils, which seem to have been u nnoticed by previous WIMP searches, may provide an interpretation of the an omalous events recorded by the UKDMC and Saclay NaI experiments. The presen t analysis points to the necessity of taking into account surface nuclear a nd electron recoil interactions for a reliable estimate of background rejec tion factors. (C) 2000 Elsevier Science B.V. All rights reserved.