An upper limit on the $\tau$ neutrino mass from three- and five-prong tau decays

Abstract.

A bound on the tau neutrino mass is established using the data collected from 1991 to 1995 at $\sqrt{s} \simeq m_{Z}$ with the ALEPH detector. Two separate limits are derived by fitting the distribution of visible energy vs invariant mass in $\tau^{-} \rightarrow 2\pi^{-} \pi^{+} \nu_{\tau}$ and $\tau^{-} \rightarrow 3\pi^{-} 2\pi^{+} (\pi^{0}) \nu_{\tau}$ decays. The two results are combined to obtain a 95% confidence level upper limit of 18.2 MeV/c$^2$ on the mass of the tau neutrino.