Measurement of the Branching Fraction for ${\tau }^{-}\to 5{\pi }^{\pm }\left({\pi }^0\right){\nu }_{\tau }$ and an Upper Limit on the ${\nu }_{\tau }$ Mass

The branching fraction for ${\tau }^{-}\to 5{\pi }^{\pm }\left({\pi }^0\right){\nu }_{\tau }$ is measured from data accumulated with the Mark II detector at PEP. Four events are observed with an estimated hadronic background of (${0.03}_{-0.02\mathrm{}}^{+0.04\mathrm{}}$) events and a background from ${\tau }^{-}\to 3{\pi }^{\pm }{\pi }^0{\nu }_{\tau }$ of (${0.05}_{-0.04\mathrm{}}^{+0.07\mathrm{}}$) events. This results in a measured branching fraction of (0.16±0.08±0.04)%. The candidate events are used to establish an upper limit of 125 MeV/${\mathit{c}}^2$ on the ${\nu }_{\tau }$ mass at the 95% confidence level.