Wuppertal 2015 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 28: Niederenergie Neutrinophysik II

T 28.1: Vortrag

Montag, 9. März 2015, 16:45–17:00, I.12.01 (HS 30)

Excited state transitions in 2νββ decays of ⁷⁶Ge from Phase I of the GERDA experiment. — •Thomas Wester for the GERDA collaboration — IKTP, TU Dresden

The Germanium Detector Array GERDA is an experiment searching for the neutrinoless double beta decay in ⁷⁶Ge. The observation of such a decay would prove the Majorana character of the neutrino and could provide a hint about the neutrino mass and possibly identify the mass hierarchy scheme.
The half life of the neutrino accompanied double beta decay (2νββ) of ⁷⁶Ge has been measured by GERDA Phase I with unprecedented precision. The observed spectrum comes mostly from the transition from the 0⁺ ground state of ⁷⁶Ge to the 0⁺ ground state of ⁷⁶Se. However, phase space suppressed 2νββ transitions to excited states of ⁷⁶Se exist as well. At current state, the predicted half lives for such decays vary by several orders of magnitute, due to the large uncertainties in the nuclear matrix elements and the available nuclear models. An observation would therefore help to constrain model parameters and decrease those uncertainties.
This study investigates the 2νββ decay of ⁷⁶Ge into various excited states of ⁷⁶Se using the data from GERDA Phase I. An event counting method is performed based on coincident events between two germanium detectors. Several analysis parameters are optimized with the help of Monte Carlo simulations to maximize the sensitivity. The presentation will discuss the procedure and results of this analysis.