Search for nucleon decay into charged antilepton plus meson in Super-Kamiokande I and II

Abstract

Searches for a nucleon decay into a charged antilepton (${e}^{+}$ or ${\ensuremath{\mu}}^{+}$) plus a light meson (${\ensuremath{\pi}}^{0}$, ${\ensuremath{\pi}}^{\ensuremath{-}}$, $\ensuremath{\eta}$, ${\ensuremath{\rho}}^{0}$, ${\ensuremath{\rho}}^{\ensuremath{-}}$, $\ensuremath{\omega}$) were performed using the Super-Kamiokande I and II data. Twelve nucleon decay modes were searched for. The total exposure is $140.9\text{ }\text{ }\mathrm{kiloton}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{years}$, which includes a $91.7\text{ }\text{ }\mathrm{kiloton}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{year}$ exposure (1489.2 live days) of Super-Kamiokande-I and a $49.2\text{ }\text{ }\mathrm{kiloton}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{year}$ exposure (798.6 live days) of Super-Kamiokande II. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation. No significant evidence for a nucleon decay was observed in the data. Thus, lower limits on the nucleon partial lifetime at 90% confidence level were obtained. The limits range from $3.6\ifmmode\times\else\texttimes\fi{}{10}^{31}$ to $8.2\ifmmode\times\else\texttimes\fi{}{10}^{33}\text{ }\text{ }\mathrm{years}$, depending on the decay modes.