Final Results of the MAJORANA DEMONSTRATOR's Search for Double-Beta Decay of $^{76}$Ge to Excited States of $^{76}$Se

TL;DR

The MAJORANA DEMONSTRATOR searched for double-beta decay of $^{76}$Ge to excited states of $^{76}$Se, setting new half-life limits and beginning to test theoretical predictions with extensive germanium detector data.

Contribution

This study provides the strongest experimental half-life limits for six double-beta decay modes of $^{76}$Ge and initiates testing of modern nuclear theory predictions.

Findings

Set new half-life limits for six decay modes.

Probed for the first time the predicted half-lives for $2 uetaeta$ decay to the $0^+_1$ state.

Collected 98.2 kg-y of isotopic exposure.

Abstract

$^{76}$Ge can $\beta\beta$ decay into three possible excited states of $^{76}$Se, with the emission of two or, if the neutrino is Majorana, zero neutrinos. None of these six transitions have yet been observed. The MAJORANA DEMONSTRATOR was designed to study $\beta\beta$ decay of $^{76}$Ge using a low background array of high purity germanium detectors. With 98.2 kg-y of isotopic exposure, the DEMONSTRATOR sets the strongest half-life limits to date for all six transition modes. For $2\nu\beta\beta$ to the $0^+_1$ state of $^{76}$Se, this search has begun to probe for the first time half-life values predicted using modern many-body nuclear theory techniques, setting a limit of $T_{1/2}>1.5\times10^{24}$ y (90% CL).