A Study of Pulse Shape Discrimination in Scintillator Dark Matter Detectors

The existence of `dark matter' throughout the universe is now well established but its form and origin remain one of the greatest problems for modern cosmology. Particle physics posits a solution to this problem in the form of `Weakly Interacting Massive Particles' (WIMPs) which are predicted to exist by many theories extending physics beyond the standard model. The discovery of such particles would consequently have profound implications for both disciplines. Many experiments around the world are now endeavouring to achieve this goal but currently the most successful are those using scintillator detectors. This thesis describes a study of the use of Pulse Shape Discrimination (PSD) techniques to reduce the rate of electron recoil background events in scintillator dark matter experiments. The development of new classes of detector with novel pulse shape properties is described and the results of tests using elastic scattering of monoenergetic neutrons to simulate nuclear recoil signal events are presented. Monte Carlo simulations have been used to assess the performance of CASPAR, a particularly promising new technique, and the results presented here indicate that this has the potential to considerably improve dark matter sensitivity, particularly for spin dependent WIMP interactions. An analysis of 867 kg. days of data from an operational NaI(Tl) detector is described and the resulting evidence for a small population of events with anomalous pulse shape properties discussed.