Analysis techniques for background rejection at the MAJORANA DEMONSTRATOR

TL;DR

This paper discusses background rejection techniques for the MAJORANA DEMONSTRATOR, aiming to achieve ultra-low background rates in neutrinoless double beta decay searches using germanium detectors.

Contribution

It introduces specific background rejection methods and the detector design features that enable ultra-low background levels for future neutrino mass experiments.

Findings

Achieved background rate below 1 count/tonne/year.

Effective pulse shape analysis for background discrimination.

Detector design significantly reduces gamma background.

Abstract

The MAJORANA Collaboration is constructing the MAJORANA DEMONSTRATOR, an ultra-low background, 40-kg modular HPGe detector array to search for neutrinoless double beta decay in 76Ge. In view of the next generation of tonne-scale Ge-based 0nbb-decay searches that will probe the neutrino mass scale in the inverted-hierarchy region, a major goal of the MAJORANA DEMONSTRATOR is to demonstrate a path forward to achieving a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value at 2039 keV. The background rejection techniques to be applied to the data include cuts based on data reduction, pulse shape analysis, event coincidences, and time correlations. The Point Contact design of the DEMONSTRATOR 0s germanium detectors allows for significant reduction of gamma background.