Search for nucleon decay via $p\rightarrow\nu\pi^{+}$ and $n\rightarrow\nu\pi^{0}$ in 0.484 Mton-year of Super-Kamiokande data

TL;DR

This study searches for specific nucleon decay modes using extensive Super-Kamiokande data, refining models and uncertainties, but finds no evidence of decay, setting new lower bounds on nucleon lifetimes.

Contribution

It improves upon previous nucleon decay searches by increasing exposure, refining physics models, expanding fiducial volume, and including more systematic uncertainties.

Findings

No significant nucleon decay signal detected.

Lower bounds on proton and neutron lifetimes established.

Enhanced analysis methods improve sensitivity.

Abstract

We present the results of searches for nucleon decays via $p\rightarrow\nu\pi^{+}$ and $n\rightarrow\nu\pi^{0}$ 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 $3.5\times10^{32}$~yr for $p\rightarrow\nu\pi^{+}$ and $1.4\times10^{33}$~yr for $n\rightarrow\nu\pi^{0}$ at 90\% confidence level.