Event categories in the EDELWEISS WIMP search experiment

Four categories of events have been identified in the EDELWEISS-I dark matterexperiment using germanium cryogenic detectors measuring simultaneously chargeand heat signals. These categories of events are interpreted as electron andnuclear interactions occurring in the volume of the detector, and electron andnuclear interactions occurring close to the surface of the detectors(10-20 mu-mof the surface). We discuss the hypothesis that low energy surface nuclearrecoils,which seem to have been unnoticed by previous WIMP searches, mayprovide an interpretation of the anomalous events recorded by the UKDMC andSaclay NaI experiments. The present analysis points to the necessity of takinginto account surface nuclear and electron recoil interactions for a reliableestimate of background rejection factors