Pulse Shape Discrimination (PSD) in Liquid Argon

Dark Matter Experiment using Argon Pulse-shape discrimination (DEAP) 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. A 7-kg low-background LAr scintillation detector was constructed and run at Queen's University in Canada. A background rejection of 6 $\times$ $10^{-8}$ at 120-240 photo-electrons was achieved.