First Evidence for Neutrinoless Double Beta Decay of Atomic Nuclei, and Physics Beyond the Standard Model of Particle Physics

The HEIDELBERG-MOSKAU experiment is since ten years the most sensitive nuclear double beta experiment worldwide. It probes the absolute scale of the neutrino mass in the sub-eV region, and gave the first evidence for the neutrinoless decay mode. This is of fundamental importance for elementary particle physics. As a consequence lepton number is not conserved, the neutrino is a Majorana particle, and neutrino masses should be degenerate. Moreover, sharp restrictions are obtained for other fields of physics beyond the standard model, for supersymmetric models, leptoquarks, compositeness, the mass of a right-handed W boson, and a violation of Lorentz invariance and the equivalence principle in the neutrino sector.