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

The Mainz neutrino mass experiment investigates the endpoint region of the tritium β decay spectrum to determine the mass of the electron antineutrino. By the recent upgrade the former problem of dewetting T2 films has been solved and the signal-to-background-ratio was improved by a factor of 10. The latest measurement leads to mν2=−3.7±5.3stat±2.1sys eV2/c4, from which an upper limit of mν<2.8 eV/c2 (95% C.L.) is derived. Some indication for the anomaly, reported by the Troitsk group, was found, but its postulated half year period is contradicted by our data.