Pulse Shape Discrimination (PSD) in Liquid Argon from DEAP-1

DEAP (Dark Matter Experiment using Argon Pulse-shape discrimination) plans to search for WIMPs (Weakly Interacting Massive Particles) through elastic scattering on ${}^{40}$Ar. In this single-phase liquid argon (LAr) experiment discrimination of $\beta$ and $\gamma$ backgrounds from the WIMP-induced nuclear recoil signal is achieved by analyzing the pulse shape of scintillation light. The available pulse-shape discrimination (PSD) power at low energy (approx. 60 keV nuclear recoil) is examined using calibration data from DEAP-1, a 7 kg low-background LAr scintillation detector constructed at Queen's University in Canada, and compared to the required PSD for the planned 1000 kg LAr dark matter search.