The search for an additional neutrino mass eigenstate in the 2–100 eV region from 'Troitsk nu-mass' data: a detailed analysis

In this paper we present the details of our previously published results for the search for an additional neutrino mass state in the β-electron spectrum from the Troitsk nu-mass experiment. Here we present the steps of the analysis and show a set of likelihood functions obtained for each additional heavy mass value. We demonstrate how systematic errors were estimated. We also compare our results with those published recently for a similar analysis for Mainz data and try to explain why there is a factor of 2–3 difference in the sensitivity for an additional heavy mass. (paper)