Electron-nuclear recoil discrimination by pulse shape analysis

In the framework of the " ULTIMA " project, we use ultra cold superfluid 3 He bolometers for the direct detection of single particle events, aimed for a future use as a dark matter detector. One parameter of the pulse shape observed after such an event is the thermalization time constant τ b. Until now it was believed that this parameter only depends on geometrical factors and superfluid 3 He properties, and that it is independent of the nature of the incident particles. In this report we show new results which demonstrate that a difference for muon-and neutron events, as well as events simulated by heater pulses exist. The possibility to use this difference for event discrimination in a future dark matter detector will be discussed.