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

Abstract

Search results for nucleon decays $p\to e^{+}X$, $p\to \hat{I}{¼}^{+}X$, $n\to \hat{I}½{\hat{I}}^3$ (where $X$ is an invisible, massless particle) as well as dinucleon decays $np\to e^{+}\hat{I}½$, $np\to \hat{I}{¼}^{+}\hat{I}½$ and $np\to \ddot{I}{„}^{+}\hat{I}½$ 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 $\ddot{I}{„}_{p\to e^{+}X}>7.9\times 10^{32}$ years, $\ddot{I}{„}_{p\to \hat{I}{¼}^{+}X}>4.1\times 10^{32}$ years, $\ddot{I}{„}_{n\to \hat{I}½{\hat{I}}^3}>5.5\times 10^{32}$ years, $\ddot{I}{„}_{np\to e^{+}\hat{I}½}>2.6\times 10^{32}$ years, $\ddot{I}{„}_{np\to \hat{I}{¼}^{+}\hat{I}½}>2.2\times 10^{32}$ years and $\ddot{I}{„}_{np\to \ddot{I}{„}^{+}\hat{I}½}>2.9\times 10^{31}$ years at a $90\%$ confidence level are obtained. Some of these searches are novel.

6 pages, 1 figure; minor corrections, length shortened, matches published version