Dresden 2013 – scientific programme

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T: Fachverband Teilchenphysik

T 110: Experimentelle Techniken der Astroteilchenphysik 3

T 110.2: Talk

Tuesday, March 5, 2013, 17:05–17:20, HSZ-101

Pulse Shape Analysis of Enriched BEGe Detectors in Vacuum Cryostat and Liquid Argon — •Victoria Wagner — Max-Planck Institut für Kernphysik, Heidelberg, Germany

The Gerda experiment searches for the lepton number violating neutrinoless double beta (0νββ) decay of ⁷⁶Ge. Germanium diodes of BEGe type (Canberra, Belgium) made from isotopically modified material have been procured for Phase II of Gerda. They will improve the sensitivity of the experiment by additional target mass, improved energy resolution and enhanced pulse shape discrimination (PSD) against background events. The PSD efficiencies of the new enriched BEGe detectors were studied in vacuum cryostats as part of the characterization campaign at the HADES underground laboratory. For a deeper understanding of the pulse shape performance of the enriched BEGe detectors, detailed ²⁴¹Am surface scans were performed. Unexpectedly high position-dependence of the pulse shape parameter Amplitude-over-Energy was found for some of the detectors. With further investigation this effect was traced to surface charge effects specific to the operational configuration of the detectors inside the vacuum cryostats. The standard behavior is restored when they are operated in liquid argon in the configuration intended for Gerda Phase II.
Finally, five of the enriched BEGe diodes were installed in the Gerda liquid argon cryostat prior to the full upgrade. They show a good performance and are able to reject efficiently multi-site-events as well as β- and α-particles.