Double beta decay and dark matter in the Gotthard germanium experiment

An array of eight high purity Germanium crystals is operated in the Gotthard road tunnel. Based on a data sample of 6.2 kg years, limits on different modes of double beta decay in 76Ge are obtained. In particular, the half-life for the neutrinoless double beta decay to the ground state of 76Se is greater than 2.0·1023 (3.4·1023) years at the 90% (68%) confidence level. A low energy sample of 51.6 kg days was used to set limits on cold dark matter. In particular, Dirac neutrinos with masses between 10 and 2400 GeV are ruled out. A new lower limit on the half-life for the decay of the electron into weakly interacting particles of 1.9·1023 years at 68% confidence level was also derived. (author)