Search for proton decay via p→e+π0 and p→μ+π0 in a large water cherenkov detector

We have searched for proton decaysvia $p\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\pi}}^{0}$ and $p\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\pi}}^{0}$ using data from a $91.7\text{ }\text{ }\mathrm{kt}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{yr}$ exposure of Super-Kamiokande-I and a $49.2\text{ }\text{ }\mathrm{kt}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{yr}$ exposure of Super-Kamiokande-II. No candidate events were observed with expected backgrounds induced by atmospheric neutrinos of 0.3 events for each decay mode. From these results, we set lower limits on the partial lifetime of $8.2\ifmmode\times\else\texttimes\fi{}{10}^{33}$ and $6.6\ifmmode\times\else\texttimes\fi{}{10}^{33}$ years at 90% confidence level for $p\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\pi}}^{0}$ and $p\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\pi}}^{0}$ modes, respectively.