Neutrinoless double-beta decay—status of evidence and future

Double-beta decay is indispensable to solve the question of the neutrino mass matrix together with ν oscillation experiments. Recent analysis of the most sensitive experiment in the last eight years—the Heidelberg-Moscow experiment in Gran Sasso—yields evidence for the neutrinoless decay mode at a 97% C.L. This result is the first indication for lepton number violation and for the neutrino to be a Majorana particle. We give the present status of the analysis in these proceedings. It excludes several of the neutrino mass scenarios allowed from present neutrino oscillation experiments—essentially only degenerate and partially degenerate mass scenarios survive. To improve the present result, considerably enlarged experiments are required, such as GENIUS. A GENIUS Test Facility has just been funded and will come into operation by the end of 2002.