Study of the Decayτ−→π−π−π+ντ

The branching ratios for ${\tau }^{-}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}{\nu }_{\tau }$ and ${\tau }^{-}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}\left(n{\pi }^0\right){\nu }_{\tau }$, $n>~1$, have been measured to be 0.078 ± 0.005 ± 0.008 and 0.047 ± 0.005 ± 0.008, respectively. The total three-prong tau branching ratio is 0.128 ± 0.005 ± 0.008. Study of the $3{\pi }^{\pm }{\nu }_{\tau }$ decay indicates that the three pions are predominantly from a $J^P=1^{+}$ state which decays through a ${\rho }^0{\pi }^{\pm }$ intermediate state in a relative $s$ wave. The $\rho \pi$ mass spectrum is suggestive of a resonance.