Double-beta decay and the quest for Neutrino Masses

Giorgio Gratta, Professor of Physics, Stanford University

With the definite evidence for neutrino oscillations collected in the last decade, we now believe that neutrino masses are non-zero. Oscillation measurements, however, only measure mass differences and give us little information about the absolute values of neutrino masses.

The rare phenomenon of neutrino-less double-beta decay represents our best option to attempt measuring very small neutrino masses. This process, if observed, would also imply that neutrinos, unlike all other spin-1/2 particles, have only two component wave functions and that lepton number is not a conserved quantity. Following the well known principle that there is no free lunch in life, interesting half-lives for neutrino-less double-beta decay exceed 10^25 years (or 10^15 times the age of the
Universe) making experiments rather challenging. I will describe how deep mines and techniques borrowed from nuclear and particle physics, AMO and material science all contribute to this quest.