Background model for the MAJORANA DEMONSTRATOR

TL;DR

The paper discusses the development and testing of background reduction techniques for the MAJORANA DEMONSTRATOR, aiming to achieve ultra-low background levels necessary for future neutrino mass experiments.

Contribution

It introduces a comprehensive background mitigation strategy combining material purity, detector technology, and analysis methods, with preliminary results from engineering runs.

Findings

Background rate approaching target levels

Effective pulse shape analysis for background rejection

Material purity constraints inform background modeling

Abstract

The MAJORANA Collaboration is constructing a system containing 44 kg of high-purity Ge (HPGe) detectors to demonstrate the feasibility and potential of a future tonne-scale experiment capable of probing the neutrino mass scale to ~15 meV. To realize this, a major goal of the MAJORANA DEMONSTRATOR is to demonstrate a path forward to achieving a background rate at or below 1 count/(ROI-t-y) in the 4 keV region of interest (ROI) around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials and analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. The effectiveness of these methods is assessed using simulations of the different background components whose purity levels are constrained from radioassay measurements. Preliminary background results obtained during the engineering runs of the Demonstrator are presented.