e⁺/e^- discrimination in liquid scintillator and its usage to suppress ⁸He/⁹Li backgrounds

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 ⁸He/⁹Li backgrounds and improves the sensitivity by 0.6 in χ² analysis with an assumption of σ = 1 ns PMT Transit Time Spread, which will bring a smearing effect to the PETD. (authors)