Search for proton decay via $p\to e^{+}\hat{I}\cdot$ and $p\to \hat{I}{¼}^{+}\hat{I}\cdot$ with a 0.37 Mton-year exposure of Super-Kamiokande

Abstract

A search for proton decay into $e^{+}/\hat{I}{¼}^{+}$ and a $\hat{I}\cdot$ meson has been performed using data from a 0.373 Mton$\cdot$year exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear $\hat{I}\cdot$ interaction cross section, resulting in a factor of two reduction in uncertainties from this source and $\sim$10\% increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of $1.4\times 10^{34}\mathrm{years}$ for $p\to e^{+}\hat{I}\cdot$ and $7.3\times 10^{33}\mathrm{years}$ for $p\to \hat{I}{¼}^{+}\hat{I}\cdot$ at the 90$\%$ C.L. were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date.