Determination of the electron neutrino rest mass via tritium decay

University Of Texas At Austin, Austin TX

Investigators

Abstract

The experimental determination of the mass of the neutrinos (orantineutrinos) is a slow and increasingly more complex process. The electron antineutrinos are the favored object. They are produced during beta-decay, and electrons are ejected at the same time. Their properties link directly to the spin and mass of the escaping neutrino through fundamental conservation laws. The preferred beta decay source is tritium since the electrons have only 18.56 KeV energy at the endpoint of the beta spectrum. This is a value, which is technologically achievable even with meV resolution. However one is dealing with the endpoint of the beta spectrum, where the intensities of the electron fluxes per eV energy interval are down by 10 order of magnitudes. This is the quintessential problem for all experiments aimed at the direct determination of the neutrino mass. All neutrino rest mass experiments must include electron spectrometers with high resolution; ultralow dark count detectors, excellent calibration procedures, and superstabilities for all experimental parameters to collect data for very long times to cope with the statistical uncertainties. A new effort is under way at the Physics Department of The University of Texas at Austin, in cooperation with the University of Nebraska, Brandeis University, Michigan Tech University, Pomona College, and The University of Texas at Arlington. Our approach is based on a series of electrostatic electron analyzers, which are designed to record the beta electron energies with about 1 eV resolution. The source is gaseous, molecular tritium at 30K. The detectors are easily accessible and can be shielded from unwanted cosmic radiation to 1 dark count per day. There is no magnetic field inside the whole apparatus. Furthermore we will use the gas cell as a target for electron diffraction in order to calibrate the voltages at the spectrometers with the de Broglie wavelenghts of electrons produced by a telefocus electron gun. This is possible since the bond length of T2 is very well known from Raman spectroscopy. The beam electrons will also give us laso the spectrometer function to about .2 eV resolution. In summary, when all units work as designed our experiment will lead to a determination of the mass of the elctron antineutrino at the .5 eV level.