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 ν -mass” set-up during 1993–1997. Fits to the data give evidence for the existence of a bump-like structure placed 5–12 eV below end point with a relative intensity about 10−10. The comparison of the anomaly region of the spectrum measured at different time reveals a movement of the bump position back and forth with respect to end point energy. After accounting for the bump and a correction for effect of electron trapping in the source the shape of all the measured part of the beta spectrum agree with mν2 about zero thus eliminating the problem of “negative mν2”. An upper limit for the neutrino mass including only data of 1994–1996 runs is: mν < 3, 8 eV/c2 at 95% C.L.