for Heavy Neutrinos Up: Neutrino
Masses Previous: Mass
Mass limits for
These measurements apply to , the dominant mass eigenstate in .
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