Neutrino mass from tritium beta 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 dec ay spectrum with a MAC-E spectrometer to determine the mass of the electron antineutrino. By the recent upgrade at Mainz the former problem of dewetti ng T-2 films has been solved and the signal-to-background-ratio was improve d by a factor of 10, resulting in a sensitivity similar to Troitsk. The lat est 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 gr oup, was found by the Mainz group, but the postulated half year period of t he anomaly is contradicted by Mainz. To push the sensitivity on the neutrin o 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.