A search for cosmogenic production of $\beta$-neutron emitting radionuclides in water

TL;DR

This paper reports the first measurements of cosmogenic radionuclide production in water by cosmic ray muons using the WATCHBOY detector, setting upper limits on $^{9}$Li yield relevant for neutrino background estimates.

Contribution

First experimental measurement of cosmogenic radionuclide yields in water with WATCHBOY, including upper limits on $^{9}$Li production at significant depth.

Findings

$^{9}$Li production yield upper limit of $1.9\times10^{-7}\mu^{-1}g^{-1}\mathrm{cm}^2$

Detection of $^{9}$Li as a proxy for other radionuclides

Implications for background estimates in water-based neutrino detectors

Abstract

Here we present the first results of WATCHBOY, a water Cherenkov detector designed to measure the yield of $\beta$-neutron emitting radionuclides produced by cosmic ray muons in water. In addition to the $\beta$-neutron measurement, we also provide a first look at isolating single-$\beta$ producing radionuclides following muon-induced hadronic showers as a check of the detection capabilities of WATCHBOY. The data taken over $207$ live days indicates a $^{9}$Li production yield upper limit of $1.9\times10^{-7}\mu^{-1}g^{-1}\mathrm{cm}^2$ at $\sim400$ meters water equivalent (m.w.e.) overburden at the $90\%$ confidence level. In this work the $^{9}$Li signal in WATCHBOY was used as a proxy for the combined search for $^{9}$Li and $^{8}$He production. This result will provide a constraint on estimates of antineutrino-like backgrounds in future water-based antineutrino detectors.