GERDA, searching for the neutrinoless double beta decay in 76Ge

The observation of the neutrinoless double beta decay (0ν2β) would verify the commonly assumed Majorana nature of the neutrino. For a Majorana neutrino this process is possible as the neutrino oscillations proof their non-vanishing mass. Consequently, one needs to extended the Standard Model as the lepton number conservation is violated. Discovery of the 0ν2β decay could possibly resolve the hierarchy problem and set the mass scale for neutrinos. 0ν2β decay is a very rare process (T1/2> 1025 y) which therefore requires extremely low background experimental conditions. 76Ge is well suited for the calorimetric approach where source and detector are identical. The GERDA collaboration has available ∝18 kg of enriched detectors from the previous 0ν2β experiments HdM and IGEX. In contrast to these the GERDA setup relies on a different concept of background suppression: operating the bare diodes in lAr with a large water buffer around, all located at the underground laboratory LNGS. Only screened high purity material after screening is used. The setup will be completed and the measurements start in 2009.