Status of the development of surface event rejection for ionization-heat detectors in the EDELWEISS collaboration

The poor collection of free charge carriers for surface events produced by beta-, X- and gamma-rays is a strong limiting factor for dark-matter searches for WIMPs with detectors measuring ionization and heat simultaneously. For such events, electron recoils can mimic nuclear recoils generated by WIMPs. The solution is to develop position-sensitive detectors to discriminate according to the depth of the interaction as well as the ionization–heat characteristics. In this paper, we describe the status of different active rejection techniques that are under development in the EDELWEISS collaboration to identify and reject this type of event.