Search for nucleon decay via $p\to \hat{I}½\ddot{I}{€}^{+}$ and $n\to \hat{I}½\ddot{I}{€}^0$ in 0.484 Mton-year of Super-Kamiokande data

Abstract

We present the results of searches for nucleon decays via $p\to \hat{I}½\ddot{I}{€}^{+}$ and $n\to \hat{I}½\ddot{I}{€}^0$ using a 0.484 Mt$\cdot$yr exposure of Super-Kamiokande I-V data covering the entire pure water phase of the experiment. Various improvements on the previous 2014 nucleon decay search, which used an exposure of 0.173 Mt$\cdot$yr, are incorporated. The physics models related to pion production and nuclear interaction are refined with external data, and a more comprehensive set of systematic uncertainties, now including those associated with the atmospheric neutrino flux and pion production channels is considered. Also, the fiducial volume has been expanded by 21\%. No significant indication of a nucleon decay signal is found beyond the expected background. Lower bounds on the nucleon partial lifetimes are determined to be $3.5\times 10^{32}$~yr for $p\to \hat{I}½\ddot{I}{€}^{+}$ and $1.4\times 10^{33}$~yr for $n\to \hat{I}½\ddot{I}{€}^0$ at 90\% confidence level.

12 pages, 3 figures