Münster 2017 – scientific programme

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T: Fachverband Teilchenphysik

T 81: Neutrinophysik 7 (Doppelbetazerfall, sterile Neutrinos)

T 81.1: Group Report

Wednesday, March 29, 2017, 16:45–17:05, VSH 118

Background free search for neutrinoless double beta decay with Gerda Phase II — •Christoph Wiesinger for the GERDA collaboration — Physik-Department and Excellence Cluster Universe, Technische Universität München, James-Franck-Straße, 85748 Garching

An observation of neutrinoless double beta decay would allow to shed light onto the nature of neutrinos. Gerda (GERmanium Detector Array) is operating isotopically enriched high purity germanium detectors bare in liquid argon and is aiming to perform a background-free search for this process in ⁷⁶Ge. A signal would manifest in a monoenergetic peak in the summed electron spectrum. Gerda is located at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy and follows a staged approach. In Phase II 35.6 kg of enriched germanium detectors are operated. The application of active background rejection methods, such as a liquid argon scintillation light read-out and pulse shape discrimination of germanium detector signals, allowed to reduce the background index to the intended level of 10⁻³ cts/(keV·kg·yr). In the first five month 10.8 kg·yr of exposure were accumulated. No signal has been found and together with data from Phase I a new limit for the neutrinoless double beta decay half-life of ⁷⁶Ge of 5.3·10²⁵ yr at 90% C.L. was established in June 2016. Phase II data taking is ongoing and will allow the exploration of half-lifes in the 10²⁶ yr regime. The current status of the blinded data taking and an update on the background index will be presented. This work was partly funded by BMBF.