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

TL;DR

This study searches for proton decay into specific channels using Super-Kamiokande data over 19 years, setting new lower limits on proton lifetime and improving background suppression techniques.

Contribution

The paper introduces new signal criteria and background reduction methods, enhancing the sensitivity of proton decay searches in water Cherenkov detectors.

Findings

No proton decay candidates found in $p ightarrow e^+ \pi^0$ channel.

Two candidates observed in $p ightarrow \mu^+ \\pi^0$ channel are consistent with background.

Proton lifetime lower limits set at $1.6 imes 10^{34}$ and $7.7 imes 10^{33}$ years for the two decay modes.

Abstract

We have searched for proton decay via $p \rightarrow e^{+} \pi^{0}$ and $p \rightarrow \mu^{+} \pi^{0}$ 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 $p \rightarrow e^{+} \pi^{0}$ search. Two candidates that passed all of the selection criteria for $p \rightarrow \mu^{+} \pi^{0}$ 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 $\tau/B(p \rightarrow e^{+} \pi^{0}) > 1.6 \times 10^{34}$ years and $\tau/B(p \rightarrow \mu^{+} \pi^{0}) > 7.7 \times 10^{33}$ years at 90% confidence level.