The EXO program and the quest for Majorana Neutrino Masses

by Giorgio Gratta (Physics Department, Stanford Univ.)

Thursday 20 Feb 2014, 10:00 → 11:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Edificio G. Marconi)

With the definitive 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 hypothetical phenomenon of neutrino-less double-beta decay can probe the neutrino mass scale with exquisite sensitivity.   This process, if observed, would also imply that neutrinos, unlike all other spin-1/2 particles, are of the Majorana type, that is they have wave functions with only two compenents.  The observation of the neutrino-less double-beta decay would also imply the non-conservation of the lepton number. 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 the the EXO program, including the recent measurements by EXO-200 that establish the present state of the art and the plans for a 5-ton enriched Xe detector, nEXO, that will have a sensitivity to Majorana masses below 10meV.