Branching ratios for deexcitation processes of daughter nuclei following invisible dinucleon decays in 16O

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 16O nucleus. To this end, we use a simple shell model for the ground state of 16O. For decays from the 1s1/2 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 16O, respectively. In particular, emission of 6.09 MeV and 7.01 MeV gamma-rays from 14C, and 6.45 MeV and 7.03 MeV gamma-rays from 14N, have branching ratios as large as 10.9%, 20.1%, 7.73% and 8.90%, respectively.