Mitigation of $^{42}$Ar/$^{42}$K background for the GERDA Phase II experiment

TL;DR

This paper discusses methods to significantly reduce $^{42}$K background in the GERDA Phase II experiment, enhancing its sensitivity to neutrinoless double beta decay detection.

Contribution

It introduces a combined suppression technique using ion collection reduction, pulse shape discrimination, and scintillation vetoes to mitigate $^{42}$K background.

Findings

Achieved three orders of magnitude suppression of $^{42}$K background.

Demonstrated effectiveness of combined suppression techniques at LArGe facility.

Confirmed suppression methods are sufficient for GERDA Phase II requirements.

Abstract

Background coming from the $^{42}$Ar decay chain is considered to be one of the most relevant for the GERDA experiment, which aims to search of the neutrinoless double beta decay of $^{76}$Ge. The sensitivity strongly relies on the absence of background around the Q-value of the decay. Background coming from $^{42}$K, a progeny of $^{42}$Ar, can contribute to that background via electrons from the continuous spectrum with an endpoint of 3.5 MeV. Research and development on the suppression methods targeting this source of background were performed at the low-background test facility LArGe. It was demonstrated that by reducing $^{42}$K ion collection on the surfaces of the broad energy germanium detectors in combination with pulse shape discrimination techniques and an argon scintillation veto, it is possible to suppress the $^{42}$K background by three orders of magnitude. This is sufficient for Phase II of the GERDA experiment.