An upper limit on additional neutrino mass eigenstate in 2 to 100 eV   region from "Troitsk nu-mass" data
  We performed a search for any sign of an additional neutrino mass state in beta-electron spectrum based on data reanalysis of direct electron antineutrino mass measurements in Tritium beta-decay in the Troitsk nu-mass experiment. The existing data set allows us to search for such a state in the mass range up to 100 eV. The lowest value at a 95% C.L. upper limit for the contribution of a heavy eigenstate into electron neutrino is around or less than 1% for masses above 20 eV. 
A. I. Belesev, A. I. Berlev, E. V. Geraskin, A. A. Golubev, N. A.   Likhovid, A. A. Nozik, V. S. Pantuev, V. I. Parfenov, A....
hep-ex hep-ph