A limit on the tau neutrino mass is obtained using all the $Z^{ 0} \to \tau^{ +} \tau^{ -}$ 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 $\tau$ 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 $m^{ *}_{ 5 \pi}$ and on the energy $E_{ 5 \pi}$ of the f{ }ive $\pi^{ \pm}$ system. The result found is $m_{ \nu_{ \tau}}<$ 48.0 MeV/$c^{ 2}$ at 95% conf{ }idence level.
Categories: hep-ex