e$^{+}$/e$^{-}$ Discrimination in Liquid Scintillator and Its Usage to Suppress $^{8}$He/$^{9}$Li Backgrounds

TL;DR

This paper presents a method to distinguish positron-electron pairs from other signals in liquid scintillator detectors, using positronium lifetime and photon emission timing, to reduce background noise in neutrino experiments.

Contribution

It introduces a new PSD parameter based on photon emission time distribution and demonstrates its application in suppressing specific backgrounds in the JUNO neutrino experiment.

Findings

Positronium lifetime measured at 3.1 ns.

Discrimination improves sensitivity by 0.6 in chi-squared analysis.

Effective background suppression with PETD-based PSD.

Abstract

Reactor neutrino experiments build large-scale detector systems to detect neutrinos. In liquid scintillator, a neutral bound state of a positron and an electron, named positronium, can be formed. The spin triplet state is called ortho-positronium (o-Ps). In this article, an experiment is designed to measure the lifetime of o-Ps, giving a result of 3.1 ns. A PSD parameter based on photon emission time distribution (PETD) was constructed to discriminate e$^+$/e$^-$. Finally, the application of e$^+$/e$^-$ discrimination in the JUNO experiment is shown. It helps suppress $^{8}$He/$^{9}$Li backgrounds and improves the sensitivity by 0.6 in $\chi^2$ analysis with an assumption of $\sigma$=1 ns PMT Transit Time Spread, which will bring a smearing effect to the PETD.