Observation ofτ-Lepton Decay to Five Charged Particles

Abstract

The production of $\tau$-lepton pairs in $e^{+}{e}^{-}$ collisions at 29 GeV has been used to study the inclusive $\tau$ decay into five charged particles. Ten events are observed in the high-resolution spectrometer giving a branching ratio of $B(\tau \to 5{\pi }^{\pm }+n\gamma +{\nu }_{\tau })=(1.3\mathrm{}\pm 0.4)\times {10}^{-3\mathrm{}}$. Five of the events contain photons which are consistent with coming from a single ${\pi }^0$. With this interpretation we measure $B(\tau \to 5{\pi }^{\pm }+{\nu }_{\tau })$, $B(\tau \to 5{\pi }^{\pm }+{\pi }^0+{\nu }_{\tau })=(6.7\mathrm{}\pm 3.0)\times {10}^{-4\mathrm{}}$. The branching-ratio upper limit for the decay mode $\tau \to K^0+3\mathrm{}{\pi }^{\pm }+n\gamma +{\nu }_{\tau }$ is found, at 90% confidence level, to be 2.7×${10}^{-3\mathrm{}}$.