Search for invisible modes of nucleon decay in water with the SNO+ detector

Abstract

This paper reports results from a search for nucleon decay through invisible modes, where no visible energy is directly deposited during the decay itself, during the initial water phase of $\mathrm{SNO}+$. However, such decays within the oxygen nucleus would produce an excited daughter that would subsequently deexcite, often emitting detectable gamma rays. A search for such gamma rays yields limits of $2.5\ifmmode\times\else\texttimes\fi{}{10}^{29}\text{ }\text{ }\mathrm{y}$ at 90% Bayesian credibility level (with a prior uniform in rate) for the partial lifetime of the neutron, and $3.6\ifmmode\times\else\texttimes\fi{}{10}^{29}\text{ }\text{ }\mathrm{y}$ for the partial lifetime of the proton, the latter a 70% improvement on the previous limit from SNO. We also present partial lifetime limits for invisible dinucleon modes of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{28}\text{ }\text{ }\mathrm{y}$ for $nn$, $2.6\ifmmode\times\else\texttimes\fi{}{10}^{28}\text{ }\text{ }\mathrm{y}$ for $pn$ and $4.7\ifmmode\times\else\texttimes\fi{}{10}^{28}\text{ }\text{ }\mathrm{y}$ for $pp$, an improvement over existing limits by close to 3 orders of magnitude for the latter two.