Mainz 2012 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 40: Astroteilchenphysik

HK 40.4: Talk

Thursday, March 22, 2012, 17:45–18:00, RW 3

Investigations of the ⁴²Ar background in the LArGe test facility for the GERDA experiment — •Alexey Lubashevskiy — Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg, Germany

Gerda is an ultra-low background experiment aimed to search for the neutrinoless double beta decay of ⁷⁶Ge. The main concept of Gerda is the operation of naked HPGe detectors made from enriched ⁷⁶Ge, which are immersed in liquid argon (LAr). During the first commissioning runs it was found that cosmogenically produced ⁴²Ar can contribute considerably to the background near the region of interest and the count rate due to decay of its daughter isotope ⁴²K is much higher than expected. It can happen when charged ⁴²K ions are collected by the applied electric field on the detector surfaces. Detailed investigations of the distribution and the behaviour of ⁴²K ions in the LAr under different configurations of the electric field were performed in the low-background test facility LArGe. For this purpose the encapsulated germanium detector GTF-44 was operated in 1 m³ of LAr in the LArGe setup. By applying different voltage on the encapsulation it is possible to attract or repel charged ions. Moreover, particle decays which deposit part of their energy in LAr can be detected by the scintillation signal using 9 PMTs. In order to increase the statistics and clearly see the effects the LAr was spiked with about 5 Bq of specially produced ⁴²Ar. This allowed to investigate the collection process of ⁴²K and to optimize methods for the suppression of the background from ⁴²Ar.