NEUTRINO REST MASS AND ANOMALY IN THE TRITIUM BETA-SPECTRUM

The end point region of the tritium beta-spectrum has been studied on the ''Troitsk nu-mass'' set-up during 1993-1997. Fits to the data give evidence for the existence of a bump-like structure placed 5-12 eV be low end point with a relative intensity about 10(-10). The comparison of the anomaly region of the spectrum measured at different time revea ls a movement of the bump position back and forth with respect to end point energy. After accounting for the bump and a correction for effec t of electron trapping in the source the shape of all the measured par t of the beta spectrum agree with m(nu)(2), about zero thus eliminatin g the problem of ''negative m(nu)(2n). An upper limit for the neutrino mass including only data of 1994-1996 runs is : m(nu) < 3, 8 eV/c(2) at 95 % C.L.