Neutrino mass from tritium β decay -: Present limits and perspectives

Tritium beta decay experiments are currently running in Mainz and Troitsk. Both experiments are investigating the endpoint region of the tritium a decay spectrum with a MAC-E spectrometer to determine the mass of the electron antineutrino. By the recent upgrade at Mainz the former problem of dewetting T-2 films has been solved and the signal-to-background-ratio was improved by a factor of 10, resulting in a sensitivity similar to Troitsk. The latest Mainz measurement in 1998 leads to m(nu)(2) = -3.7 +/- 5.3(stat) +/- 2.1(sys) eV(2)/c(4), from which an upper limit of m(nu) < 2.8 eV/c(2) (95% C.L.) is derived. Some indication for the anomaly, reported by the Troitsk group, was found by the Mainz group, but the postulated half year period of the anomaly is contradicted by Mainz. To push the sensitivity on the neutrino mass below 1 eV/c(2) a new larger MAC-E spectrometer is proposed. Besides its integrating mode it could run in a new non-integrating operation MAC-E-TOF mode.