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

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.

6 pages,8 figures