Progress Toward A $2νββ$ Measurement For The Majorana Demonstrator

Abstract

The MAJORANA DEMONSTRATOR is a $^{76}$Ge-based neutrinoless double-beta decay ($0νββ$) experiment. Staged at the 4850 ft level of the Sanford Underground Research Facility, the DEMONSTRATOR operates an array of high-purity p-type point contact Ge detectors deployed within a graded passive shield and an active muon veto system. The present work concerns the two-neutrino double-beta decay mode ($2νββ$) of $^{76}$Ge. For Ge detectors, having superior energy resolution (0.1%), this mode poses negligible background to the $0νββ$ mode, even for a ton-scale experiment. However, the measurement of the $2νββ$ mode allows for careful systematics checks of active detector mass, enrichment fraction, and pulse shape discrimination cuts related to both the $0νββ$ and $2νββ$ decay modes. A precision measurement of the $2νββ$ shape also allows searches for spectral distortions, possibly indicative of new physics, including $0νββχ$. Work is underway to construct a full experimental background model enabling a Bayesian fit to the measured energy spectrum and extraction of a precise $2νββ$ spectrum and half-life.

5 pages, 2 figures, TAUP 2017: XV International Conference on Topics in Astroparticle and Underground Physics