Technique for direct detection of weakly interacting massive particles using scintillation time discrimination in liquid argon

Discrimination between electron and nuclear recoil events in a liquid argon scintillation detector has been demonstrated with simulations by using the differences in the scintillation photon time distribution between these classes of events. A discrimination power greater than 108 is predicted for a liquid argon experiment with a 10 keV threshold, which would mitigate electron and γ-ray backgrounds, including β decays of 39Ar and 42Ar in atmospheric argon. A dark matter search using a ∼2 kg argon target viewed by immersed photomultiplier tubes would allow a sensitivity to a spin-independent WIMP-nucleon cross-section of ∼10−43 cm2 for a 100 GeV WIMP, assuming a one-year exposure. This technique could be used to scale the target mass to the tonne scale, allowing a sensitivity of ∼10−46 cm2.