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Abstract:
LArGe is a Gerda low-background test facility to study novel background suppression
methods in a low-background environment, for possible applications in the Gerda experiment.
Gerda searches for the neutrinoless double-beta decay in 76Ge, by operating
naked germanium detectors submersed into 65 m3 of liquid argon. Similarly, LArGe runs
Ge-detectors in 1 m3 (1.4 tons) of liquid argon, which in addition is instrumented with
photomultipliers to detect argon scintillation light. The light is used in anti-coincidence
with the germanium detectors, to effectively suppress background events that deposit energy
in the liquid argon. This work adresses the design, construction, and commissioning of
LArGe. The background suppression efficiency has been studied in combination with a
pulse shape discrimination (PSD) technique for various sources, which represent characteristic
backgrounds to Gerda. Suppression factors of a few times 103 have been achieved.
First background data of LArGe (without PSD) yield a background index of (0.12-4.6)·10−2
cts/(keV·kg·y) (90% c.l.), which is at the level of the Gerda phase I design goal. Furthermore,
for the first time we measure the natural 42Ar abundance (in parallel to Gerda),
and have indication for the 2νββ-decay in natural germanium.
