Limits on $ν_τ$ mass by DELPHI

Abstract

A limit on the tau neutrino mass is obtained using all the $Z^{0} \to τ^{+} τ^{-}$ data collected at LEP by the DELPHI detector between 1992 and 1995. In this analysis events in which one of the taus decays into one charged particle, while the second $τ$ decays into f{}ive charged pions (1-5 topology) have been used. The neutrino mass is determined from a bidimensional \fit ~on the invariant mass $m^{*}_{5 π}$ and on the energy $E_{5 π}$ of the f{}ive $π^{\pm}$ system. The result found is $m_{ν_τ}<$ 48.0 MeV/$c^{2}$ at 95% conf{}idence level.