PNNL

Abstract

The Majorana Demonstrator is a 76Ge-based neutrinoless double-beta decay (0vßß) 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 (2vßß) of 76Ge. For Ge detectors, with superior energy resolution (0.1%), this mode poses negligible background to the 0vßß mode, even for a ton-scale experiment. However, the measurement of the 2vßß mode allows for careful systematics checks of active detector mass, enrichment fraction, and pulse shape discrimination cuts related to both the 0vßß and 2vßß decay modes. A precision measurement of the 2vßß shape also allows searches for new physics such as Majoron-accompanied 0vßß.Work is underway to construct a full experimental background model enabling a Bayesian fit to the measured energy spectrum and extraction of a precise 2vßß spectrum and half-life.