Search for Proton Decay via $p\to e^{+}{\pi }^0$ and $p\to {\mu }^{+}{\pi }^0$ in 0.31 megaton$\cdot$years exposure of the Super-Kamiokande Water Cherenkov Detector

Abstract

We have searched for proton decay via $p\to e^{+}{\pi }^0$ and $p\to {\mu }^{+}{\pi }^0$ using Super-Kamiokande data from April 1996 to March 2015, 0.306 megaton$\cdot$years exposure in total. The atmospheric neutrino background rate in Super-Kamiokande IV is reduced to almost half that of phase I-III by tagging neutrons associated with neutrino interactions. The reach of the proton lifetime is further enhanced by introducing new signal criteria that select the decay of a proton in a hydrogen atom. No candidates were seen in the $p\to e^{+}{\pi }^0$ search. Two candidates that passed all of the selection criteria for $p\to {\mu }^{+}{\pi }^0$ have been observed, but these are consistent with the expected number of background events of 0.87. Lower limits on the proton lifetime are set at $\tau /B(p\to e^{+}{\pi }^0)>1.6\times 10^{34}$ years and $\tau /B(p\to {\mu }^{+}{\pi }^0)>7.7\times 10^{33}$ years at 90% confidence level.

11 pages, 5 figures

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