Search for proton decay into a single charged antilepton and a massless invisible particle using the full pure water data set of Super-Kamiokande

A search for proton decay via p → l + + X , where l + is a positively charged lepton and X is an invisible, massless, neutral particle, was performed using a 401 kton · years exposure representing the entire pure water phase of Super-Kamiokande. No significant indication of a proton decay was observed beyond the expected atmospheric neutrino background. Lower limits on the partial lifetime of the proton were set to 1.72 × 10 33 years for p → e + + X and 0.61 × 10 33 years for p → μ + + X at the 90% confidence level. These results improve on previous limits by factors of 2 and 1.5, respectively.