We propose a new experiment to search for a sterile neutrino in a few keV mass range at the "Troitsk nu-mass" facility. The expected signature corresponds to a kink in the electron energy spectrum in tritium beta-decay. The new goal compared to our previous experiment will be precision spectrum measurements well below end point. The experimental installation consists of a windowless gaseous tritium source and a high resolution electromagnetic spectrometer. We estimate that the current bounds on the sterile neutrino mixing parameter can be improved by an order of magnitude in the mass range under 5 keV without major upgrade of the existing equipment. Upgrades of calibration, data acquisition and high voltage systems will allow to improve the bounds by another order of magnitude.

We present the first results of precision measurements of tritium β-decay spectrum in the electron energy range 16-18.6 keV by the Troitsk nu-mass experiment. The goal is to find distortions which may be caused by the existence of a 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 a new upper limits to the neutrino mixing matrix element U 2 e4 which improve existing limits by a factor from 2 to 5 in the mass range 0.1-2 keV.

We've performed precise measurements of electron scattering on molecular hydrogen and deuterium by using the "Troitsk nu-mass" setup. Electrons were generated by the electron gun with an energy line width better than 0.3 eV. The electron energies were 14, 17, 18.7, 19 and 25 keV. The windowless gaseous tritium source (WGTS) was filled by hydrogen isotopes and served as a target. The total column density was adjusted to form a length of 0.35-0.7 of the electron mean free path. The integral spectrum of scattered electrons was measured by the electrostatic spectrometer with a magnetic adiabatic collimation and relative energy resolution 8.3·10 −5 . As a result, the shapes of molecular excitation and ionization spectra were extracted for both isotopes. We did not find any difference between hydrogen and deuterium targets. The relative energy dependence was extracted too.