Search for Zero-Neutrino Double Beta Decay in 76Ge with the Majorana Demonstrator

TL;DR

The Majorana Demonstrator searches for neutrinoless double-beta decay in germanium-76, achieving high energy resolution and low background, setting new limits on the decay half-life and neutrino mass.

Contribution

This paper reports the first results from the Majorana Demonstrator, demonstrating unprecedented energy resolution and background suppression in the search for neutrinoless double-beta decay.

Findings

No candidate events observed in 10 kg yr exposure.

Lower limit on decay half-life set at 1.9×10^{25} years.

Background level achieved is 4.0 counts/(FWHM t yr).

Abstract

The \MJ\ Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-beta decay in $^{76}$Ge. The \MJ\ \DEM\ comprises 44.1~kg of Ge detectors (29.7 kg enriched in $^{76}$Ge) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at \qval\ and a very low background with no observed candidate events in 10 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of $1.9\times10^{25}$ yr (90\% CL). This result constrains the effective Majorana neutrino mass to below 240 to 520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is $4.0_{-2.5}^{+3.1}$ counts/(FWHM t yr).