Search for nucleon decay via p → νπ+ and n → νπ0 in 0.484 Mton-year of Super-Kamiokande data

We present the results of searches for nucleon decays via p → νπþ and n → νπ0 using a 0.484 Mt · 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 [Phys. Rev. Lett. 113, 121802 (2014)], which used an exposure of 0.173 Mt · 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 × 1032 yr for p → νπþ and 1.4 × 1033 yr for n → νπ0 at 90% confidence level.