High precision measurement of the tritium beta spectrum near its endpoint and upper limit on the neutrino mass

The Mainz neutrino mass experiment investigates the endpoint region of the tritium beta decay spectrum to determine the mass of the electron antineutr ino. By the recent upgrade the former problem of dewetting T-2 films has be en solved and the signal-to-background-ratio was improved by a factor of 10 . The latest measurement 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.) i s derived. Some indication for the anomaly, reported by the Troitsk group, was found, but its postulated half year period is contradicted by our data. (C) 1999 Published by Elsevier Science B.V. All rights reserved.