LArGe - Active background suppression using argon scintillation for the GERDA $0\nu\beta\beta$-experiment

TL;DR

LArGe demonstrates effective active background suppression using argon scintillation light in a low-background environment, achieving suppression factors of thousands and comparable background levels to GERDA Phase I, supporting future use in neutrinoless double beta decay experiments.

Contribution

The paper introduces a novel active background suppression method using liquid argon scintillation in a low-background test facility, with results applicable to the GERDA experiment.

Findings

Suppression factors of a few thousand achieved.

Background index comparable to GERDA Phase I.

First monitoring of natural $^{42}$Ar and indication of $2 uetaeta$-decay.

Abstract

LArGe is a GERDA low-background test facility to study novel background suppression methods in a low-background environment, for future application in the GERDA experiment. Similar to GERDA, LArGe operates bare germanium detectors submersed into liquid argon (1 m$^3$, 1.4 tons), which in addition is instrumented with photomultipliers to detect argon scintillation light. The scintillation signals are used in anti-coincidence with the germanium detectors to effectively suppress background events that deposit energy in the liquid argon. The background suppression efficiency was studied in combination with a pulse shape discrimination (PSD) technique using a BEGe detector for various sources, which represent characteristic backgrounds to GERDA. Suppression factors of a few times $10^3$ have been achieved. First background data of LArGe with a coaxial HPGe detector (without PSD) yield a background index of (0.12$-$4.6)$\cdot 10^{-2}$ cts/(keV$\cdot$kg$\cdot$y) (90% C.L.), which is at the level of GERDA Phase I. Furthermore, for the first time we monitor the natural $^{42}$Ar abundance (parallel to GERDA), and have indication for the $2\nu\beta\beta$-decay in natural germanium. These results show the effectivity of an active liquid argon veto in an ultra-low background environment. As a consequence, the implementation of a liquid argon veto in GERDA Phase II is pursued.