A study of liquid argon detector’s n / γ discrimination capability with PMT or SiPM readout

Background Liquid Argon (LAr) is used as a target material in several current and planned experiments related to dark matter direct searching and neutrino detection. Argon provides excellent pulse shape discrimination (PSD) capability, which could separate the electron recoil backgrounds from the expected nuclear recoil signals. As the next-generation photosensors, silicon photon multiplier (SiPM) is expected to replace traditional photon multiplier tubes. Purpose The purpose of this paper is to compare the PSD capability of a LAr detector between using SiPMs as photosensors and using PMTs as photosensors. Methods The PSD capability of a LAr detector is determined through the prompt fraction method, which relies on the analysis of output pulses. These pulses are generated using Monte Carlo simulation, incorporating real single photoelectron pulses obtained from a PMT or a SiPM. Results Three kinds of SiPMs and one kind of PMT have been used to compare the PSD capability of a LAr detector. The use of J-60035 SiPM results in a better PSD capability compared to the use of PMT as a photosensor, while using the other two kinds of SiPM deteriorates the PSD capability. Conclusion SiPM is a promising photosensor candidate for a LAr detector. The better energy resolution could help to improve its PSD capability, while the higher probabilities of cross-talk and after-pulse degrade its PSD capability. Notably, after-pulse has a more significant impact compared to cross-talk because after-pulse influences the energy distribution within the time window, while cross-talk primarily affects the energy resolution of the detector.