Search for Tri-Nucleon Decay in the Majorana Demonstrator

Abstract

The Majorana Demonstrator is an ultra low-background experiment searching for neutrinoless double-beta decay in ${}^{76}$Ge. The heavily shielded array of germanium detectors, placed nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, also allows searches for new exotic physics. We present the first limits for tri-nucleon decay-specific modes and invisible decay modes for Ge isotopes. We find a half-life limit of $4.9\times 10^{25}$ yr for the decay ${}^{76}\mathrm{Ge}(\mathrm{ppn})\to {}^{73}\mathrm{Zn}{e}^{+}\ddot{I}{€}^{+}$ and $4.7\times 10^{25}$ yr for the decay ${}^{76}\mathrm{Ge}(\mathrm{ppp}){\to }^{73}\mathrm{Cu}{e}^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{+}$. The half-life limit for the invisible tri-proton decay mode of ${}^{76}$Ge was found to be $7.5\times 10^{24}$ yr.

Updated after suggested figure additions from referees