Scintillation-only Based Pulse Shape Discrimination for Nuclear and Electron Recoils in Liquid Xenon

TL;DR

This study demonstrates a pulse shape discrimination method in liquid xenon that effectively reduces electron background in dark matter detection by analyzing scintillation light timing, with promising results at various light yields.

Contribution

The paper introduces a simple ratio-based pulse shape discrimination technique in liquid xenon that improves background rejection in dark matter searches.

Findings

Achieved 50% nuclear recoil retention with electron background reduced to 7.7×10^-2 at 4.8-7.2 keVee

Reduced electron background to 7.7×10^-3 at 9.6-12 keVee with higher light yield

Lowering light yield to 4.6 p.e./keV still yields significant electron background reduction

Abstract

In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7\pm1.1(stat)\pm1.2 0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee and to 7.7\pm2.8(stat)\pm2.5 2.8(sys)\times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4\pm0.2(stat)\pm0.3 0.2(sys)\times10-1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.