Search for Heavy Neutrinos  Neutrino Masses  Mass limits for

Mass limits for $\nu_\tau$

These measurements apply to , the dominant mass eigenstate in $\nu_\tau$. Upper limits of this mass have been derived from studies of the decay of the tau lepton. The most sensitive results were obtained by fitting the invariant mass spectrum of hadrons produced in tau decays with a likelihood method. Up to now no indication for a finite neutrino mass for has been found. The ARGUS group analyzed 20 events of the decay . CLEO II sampled 60 events of the same type as ARGUS as well as 53 tau decays of the mode . In a recent publication a new limit on the tau neutrino mass of 24 MeV (95% CL) was reported by the ALEPH group at LEP. Here a two dimensional likelihood fit in the variables invariant mass and energy of the hadrons in decays. This method improves the sensitivity with respect to the use of invariant mass alone.