Where does double-beta decay come in?
Several experiments (including one performed at the Homestake mine!) have already demonstrated that neutrinos have some mass. In fact, they have determined the differences between the masses of the three types of neutrinos (electron, muon, and tau neutrinos). This demonstration is itself evidence that our understanding of neutrinos in the Standard Model of particle physics is incomplete. A sensitive method is now needed to determine the mass of one of the neutrino types to understand them all. Neutrinoless double-beta decay can determine the absolute scale of the electron neutrino mass.
