Spectral analysis for the Majorana Demonstrator experiment

TL;DR

This paper discusses the spectral analysis techniques used in the Majorana Demonstrator experiment, which searches for neutrinoless double-beta decay in germanium-76, highlighting background reduction and statistical methods for signal detection.

Contribution

It introduces spectral analysis methods tailored for the Majorana Demonstrator, including background reduction strategies and statistical approaches for detecting rare decay signals.

Findings

Background index reduced around the ROI due to shielding improvements

Statistical methods developed for signal hypothesis testing

Sensitivity estimates for future exposure levels

Abstract

The MAJORANA DEMONSTRATOR is an experiment constructed to search for neutrinoless double-beta decays in germanium-76 and to demonstrate the feasibility to deploy a ton-scale experiment in a phased and modular fashion. It consists of two modular arrays of natural and $^{76}\textrm{Ge}$-enriched germanium detectors totaling 44.1 kg (29.7 kg enriched detectors), located at the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA. Data taken with this setup since summer 2015 at different construction stages of the experiment show a clear reduction of the observed background index around the ROI for $0\nu\beta\beta$-decay search due to improvements in shielding. We discuss the statistical approaches to search for a $0\nu\beta\beta$-signal and derive the physics sensitivity for an expected exposure of $10\,\textrm{kg}{\cdot}\textrm{y}$ from enriched detectors using a profile likelihood based hypothesis test in combination with toy Monte Carlo data.