Scintillation time dependence and pulse shape discrimination in liquid argon

TL;DR

This paper investigates the scintillation time dependence in liquid argon for electronic and nuclear recoils, developing pulse shape discrimination methods to improve dark matter detection sensitivity.

Contribution

It introduces two pulse shape discrimination techniques based on scintillation time profiles and predicts enhanced WIMP detection sensitivity.

Findings

Achieved a background contamination level of 7.6×10⁻⁷ for electronic recoils.

Measured scintillation time dependence down to 5 keVee.

Developed a maximum likelihood method for pulse shape discrimination.

Abstract

Using a single-phase liquid argon detector with a signal yield of 4.85 photoelectrons per keV of electronic-equivalent recoil energy (keVee), we measure the scintillation time dependence of both electronic and nuclear recoils in liquid argon down to 5 keVee. We develop two methods of pulse shape discrimination to distinguish between electronic and nuclear recoils. Using one of these methods, we measure a background and statistics-limited level of electronic recoil contamination to be $7.6\times10^{-7}$ between 60 and 128 keV of nuclear recoil energy (keVr) for a nuclear recoil acceptance of 50% with no nuclear recoil-like events above 72 keVr. Finally, we develop a maximum likelihood method of pulse shape discrimination using the measured scintillation time dependence and predict the sensitivity to WIMP-nucleon scattering in three configurations of a liquid argon dark matter detector.