Branching ratios for deexcitation processes of daughter nuclei following invisible dinucleon decays in $^{16}$O

TL;DR

This paper estimates the branching ratios of gamma-ray emissions following dinucleon decays in oxygen-16, providing crucial data for detecting baryon number violation in water Cherenkov experiments.

Contribution

It introduces a shell model combined with the Hauser-Feshbach statistical approach to calculate deexcitation branching ratios after dinucleon decay in $^{16}$O.

Findings

Branching ratio for gamma-ray emission between 5-9 MeV is 4.53% for nn decay.

Branching ratios for specific gamma-rays from $^{14}$C and $^{14}$N are as high as 20%.

Results aid in interpreting signals in water Cherenkov detectors like SNO+.

Abstract

Various theories beyond the standard model of particle physics predict the existence of baryon number violating processes resulting in nucleon decay. When occurring within an atomic nucleus, such a decay will be followed by secondary decays of the daughter nucleus unless its ground state is directly populated. In this paper, we estimate branching ratios for processes associated with dinucleon decays of the $^{16}$O nucleus. To this end, we use a simple shell model for the ground state of $^{16}$O. For decays from the 1$s_{1/2}$ configuration, which result in highly excited states in the daughter nucleus, we employ a statistical model with the Hauser-Feshbach theory. Our analysis indicates that the branching ratio for gamma-ray emission in the energy range between 5 and 9 MeV, which is relevant to low-threshold water Cherenkov experiments such as SNO+, is 4.53%, 35.7%, and 20.2% for the $nn$, $pp$, and $pn$ decays in $^{16}$O, respectively. In particular, emission of 6.09 MeV and 7.01 MeV gamma-rays from $^{14}$C, and 6.45 MeV and 7.03 MeV gamma-rays from $^{14}$N, have branching ratios as large as 10.9%, 20.1%, 7.73% and 8.90%, respectively.