Direct searches for neutrino mass

Abstract

At present there is no positive experimental evidence that neutrinos have mass. Nevertheless, searches for neutrino mass continue, largely because the consequences of neutrinos having mass would be quite profound. In particular, the discovery of a non-zero neutrino mass would be a clear indication of physics beyond the current particle-physics standard model. In addition, neutrinos, if they have mass, remain viable candidates for the non-baryonic dark matter known to permeate galaxies. The current status of the experimental efforts searching for neutrino mass will be reviewed. In particular, it will be shown that the most recent tritium beta decay searches for neutrino mass clearly rule out the non-zero neutrino mass result first reported in 1980 by the Institute for Theoretical and Experimental Physics (ITEP) in Moscow. However, a troubling feature of these same recent results is that they all have best fits to neutrino mass squared that are negative. The significance of these negative neutrino mass squared results will be explored.