## Abstract

Using the ARGUS detector at the DORIS II e^{+}e^{-} storage ring we have studied the three-pion hadronic final state in the decay τ^{-} → π^{-}π^{-}π^{+}v_{τ}. From about 7500 events we conclude that the three-pion system is dominated by the J^{P}=1^{+} resonance a_{1} (1260) decaying preferentially via ρ^{0}π^{-}. Our data restrict a possible ρπ contribution of three-pion states without intermediate resonances to less than 6% at 95% CL. Fitting a model by Isgur et al. to the data yields {Mathematical expression} and {Mathematical expression}. The second errors reflect the model dependence of the result. This is the currently most significant determination of the a_{1} resonance parameters. The ratio of S- and D-wave amplitudes for the ρ^{0}π^{-} intermediate state of the a_{1}^{-} decay at the nominal a_{1}^{-} mass was found to be D/S=-0.11±0.02. Using this D/S ratio we update our former measurement of the parity violating asymmetry parameter {Mathematical expression} to 1.25±0.23±_{0.08}^{0.15}. The branching ratio of the decay τ^{-} → π^{-}π^{-}π^{+}v_{τ} is determined to be Br(τ^{-} → π^{-}π^{-}π^{+}v_{τ})=(6.8±0.1±0.5)%.

Original language | English |
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Pages (from-to) | 61-70 |

Number of pages | 10 |

Journal | Zeitschrift für Physik C Particles and Fields |

Volume | 58 |

Issue number | 1 |

DOIs | |

State | Published - Mar 1993 |

Externally published | Yes |

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