Search for Nucleon and Dinucleon Decays with an Invisible Particle and a Charged Lepton in the Final State at the Super-Kamiokande Experiment

TL;DR

This paper reports on a search for rare nucleon and dinucleon decays involving invisible particles at Super-Kamiokande, setting new lower lifetime limits and exploring some decay modes for the first time.

Contribution

It presents the first searches for certain nucleon and dinucleon decay modes involving invisible particles, establishing new lower bounds on their lifetimes.

Findings

No signal observed in the decay modes searched.

Established lower lifetime limits up to 7.9 x 10^{32} years.

Some decay modes are investigated for the first time.

Abstract

Search results for nucleon decays $p \rightarrow e^+X$, $p \rightarrow \mu^+X$, $n \rightarrow \nu\gamma$ (where $X$ is an invisible, massless particle) as well as dinucleon decays $np \rightarrow e^+\nu$, $np \rightarrow \mu^+\nu$ and $np \rightarrow \tau^+\nu$ in the Super-Kamiokande experiment are presented. Using single-ring data from an exposure of 273.4 kton $\cdot$ years, a search for these decays yields a result consistent with no signal. Accordingly, lower limits on the partial lifetimes of $\tau_{p \rightarrow e^+X} > 7.9 \times 10^{32}$ years, $\tau_{p \rightarrow \mu^+X} > 4.1 \times 10^{32}$ years, $\tau_{n \rightarrow \nu\gamma} > 5.5 \times 10^{32}$ years, $\tau_{np \rightarrow e^+\nu} > 2.6 \times 10^{32}$ years, $\tau_{np \rightarrow \mu^+\nu} > 2.2 \times 10^{32}$ years and $\tau_{np \rightarrow \tau^+\nu} > 2.9 \times 10^{31}$ years at a $90 \% $ confidence level are obtained. Some of these searches are novel.