Bonn 2020 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 28: Astroparticle Physics I

HK 28.1: Group Report

Wednesday, April 1, 2020, 14:00–14:30, J-HS B

Searching for neutrinoless double-beta decay with GERDA: results and status — •Ann-Kathrin Schütz for the GERDA collaboration — Eberhard Karls Univerität Tübingen

The GERmanium Detector Array (Gerda) experiment aims for the discovery of neutrinoless double beta decay (0νββ) decay in ⁷⁶Ge. It uses HPGe detectors enriched in the isotope ⁷⁶Ge, which are directly immersed into liquid argon (LAr). In Phase II, the radio-pure cryogenic liquid acts not only as cooling medium for the detectors and passive shielding but also as active shielding. The second phase (Phase II) of Gerda started data taking in Dec 2015 with the design goal of increasing the sensitivity to T_1/2^0ν = O( 10²⁶ )yr by reducing the background by one order of magnitude. Due to the active veto system detecting LAr scintillation light, the superior energy resolution and an improved background recognition, already the initial release of Phase II showed a background rate in the energy region of interest (ROI), after pulse shape discrimination (PSD) and liquid argon veto cuts, in the range of a few counts/(ROI·ton·yr). This made Gerda the first 0νββ experiment being background free up to its design exposure of 100 kg·yr. With the latest data release in mid 2018, Gerda remained in the background free regime. It is the first experiment to surpass a median sensitivity on the half-life of 10²⁶ yr for 0νββ decay. Meanwhile the experiment has been upgraded by deploying also a new type of germanium detector and by improving the LAr instrumentation. In this talk, a summary of the latest results and an outlook on the performance after the upgrade of the experiment will be given.