Seminarium Teorii Oddziaływań Elementarnych

Reported will be the result from the first phase of the GERDA (GERmanium Detector Array) experiment. GERDA is carried out at the Gran Sasso Laboratory of INFN in Italy and searchesfor neutrinoless double beta decay (0νββ) of 76Ge. The observation of this lepton number violating process, which is predicted by models beyond the Standard Model of particle physics, would imply that neutrinos are Majorana particles, i.e. neutrinos are their own anti-particles. Provided that the exchange of light Majorana neutrinos is the leading mechanism of neutrinoless double beta decay, measuring or constraining the half-life sheds also light on the absolute neutrino mass scale. According to the performed analysis of the Phase I data acquired between November 2011 and May 2013, the achieved background index reached the assumed 1×10-2 cts/(keV×kg×yr). No signal was observed and the derived lower limit for the half-life of the neutrinoless double beta decay of 76Ge of T1/2(0νββ) > 2.1×1025 yr (90% C.L.) is the strongest up to date. The combination with the results from the former Heidelberg–Moscow and IGEX experiments gives an improved limit of T1/2(0νββ) > 3.0×1025 yr (90% C.L.). The claim by a part of the Heidelberg–Moscow collaboration about observation of 0νββ is therefore highly disfavored. Status of preparations for GERDA Phase II will be also outlined.