Support experiments for neutrinoless double beta decay

Full text: The understanding of neutrino properties is of paramount importance for particle and astro physics. The neutrinoless double beta decay (2β0ν) is a second order weak allowed transition which violates lepton number conservation by 2 and thus leads beyond the standard model. The observation of a 2β0ν decay is the only proof of the possible Majorana nature of the neutrino. In addition, if theory provides precise matrix elements for this transition the effective neutrino mass can be deduced from the long half lives in the order of 1025 and beyond. Experimentally, background reduction and radio purity is a major task and thus these experiments are build underground. On the other hand the nuclear structure models must be tested for their reliability. As the GERDA experiment searches for the 2β0ν decay in 76Ge the present support experiments center around this mass region. Neutron capture experiments investigate the cross section and the gamma decay of 77Ge, its isomers and its daughters, as there are β and gammas emitted with energies close to Qββ. Secondly, neutron and proton transfer experiments have been performed at various facilities in order to nail down nuclear structure of the initial and final nuclei, i.e. 76Ge and 76Se. Modifications of the models are discussed. (author)