Signatures of muonic activation in the Majorana Demonstrator

TL;DR

This paper investigates muonic activation signatures in the Majorana Demonstrator to better understand cosmogenic backgrounds, using data analysis and simulations to improve background modeling for future neutrinoless double-beta decay experiments.

Contribution

It presents the first detailed analysis of muonic activation signatures in the Majorana Demonstrator, enhancing background understanding for next-generation experiments.

Findings

Good agreement between simulated and observed decay rates

Identification of decay signatures of germanium isotopes

Extended simulation framework for LEGEND background estimation

Abstract

Experiments searching for very rare processes such as neutrinoless double-beta decay require a detailed understanding of all sources of background. Signals from radioactive impurities present in construction and detector materials can be suppressed using a number of well-understood techniques. Background from in-situ cosmogenic interactions can be reduced by siting an experiment deep underground. However, the next generation of such experiments have unprecedented sensitivity goals of 10$^{28}$ years half-life with background rates of 10$^{-5}$cts/(keV kg yr) in the region of interest. To achieve these goals, the remaining cosmogenic background must be well understood. In the work presented here, Majorana Demonstrator data is used to search for decay signatures of meta-stable germanium isotopes. Contributions to the region of interest in energy and time are estimated using simulations, and compared to Demonstrator data. Correlated time-delayed signals are used to identify decay signatures of isotopes produced in the germanium detectors. A good agreement between expected and measured rate is found and different simulation frameworks are used to estimate the uncertainties of the predictions. The simulation campaign is then extended to characterize the background for the LEGEND experiment, a proposed tonne-scale effort searching for neutrinoless double-beta decay in $^{76}$Ge.