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

TL;DR

This paper proposes a fast-timing detection technique using spherical harmonics analysis to distinguish double-beta decay events from solar neutrino backgrounds in large liquid scintillator detectors, improving background rejection.

Contribution

It introduces a novel method leveraging prompt Cherenkov photons and fast photodetectors to statistically separate signal from background in kiloton-scale detectors.

Findings

Simulation shows effective discrimination between decay events and neutrino background.

Fast photodetectors with 100 ps resolution enable event topology reconstruction.

Development of slow scintillators with 5 ns risetime enhances separation capability.

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.