Separating Double-Beta Decay Events from Solar Neutrino Interactions in a Kiloton-Scale Liquid Scintillator Detector By Fast Timing

Abstract

We present a technique for separating nuclear double beta decay ($\beta \beta$-decay) events from background neutrino interactions due to ${}^8$B decays in the sun. This background becomes dominant in a kiloton-scale liquid-scintillator detector deep underground and is usually considered as irreducible due to an overlap in deposited energy with the signal. However, electrons from 0$\nu \beta \beta$-decay often exceed the Cherenkov threshold in liquid scintillator, producing photons that are prompt and correlated in direction with the initial electron direction. The use of large-area fast photodetectors allows some separation of these prompt photons from delayed isotropic scintillation light and, thus, the possibility of reconstructing the event topology. Using a simulation of a 6.5~m radius liquid scintillator detector with 100~ps resolution photodetectors, we show that a spherical harmonics analysis of early-arrival light can discriminate between 0$\nu \beta \beta$-decay signal and ${}^8$B solar neutrino background events on a statistical basis. Good separation will require the development of a slow scintillator with a 5 nsec risetime.

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