First measurements in search for keV sterile neutrino in tritium beta-decay in the Troitsk nu-mass experiment

We present the first results of precision measurements of tritium -decay spectrum in the electron energy range 16–18.6 keV by the Troitsk nu-mass experiment. The goal is to find distortions that may be caused by the existence of heavy sterile neutrinos. A signature would correspond to a kink in the spectrum with characteristic shape and end point shifted by the value of a heavy neutrino mass. We set new upper limits to the neutrino mixing matrix element U 2 , which improve existing limits by a factor of 2 to 5 in the mass range of 0.1–2 keV.