An upper limit for the

Abstract

An upper limit for the $\tau$ –neutrino mass has been determined from the decay $\tau\rightarrow 5\pi^{\pm}\nu_{\tau}$ using data collected with the OPAL detector from 1991 to 1995 in $\rm e^{+}e^{-}$ collisions at $\sqrt{s}\approx M_\mathrm{Z}$ . A limit of 43.2 MeV at 95% CL is obtained using a two–dimensional method in the $5\pi$ invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement using $\rm \tau^{+}\tau^{-}\rightarrow 3h^{\pm}\bar{\nu}_{\tau}+3h^{\mp}\nu_{\tau}$ decays, a new combined limit of $m_{\nu_{\tau}}<27.6$ MeV (95% CL) is obtained.