Measurement of the hadronic decay current in τ-→π-π-π+ντ

The decay τ- → π- π- π+ ντ has been studied using data collected with the OPAL detector at LEP during 1992 and 1993. The hadronic structure functions for this decay are measured model independently assuming G-parity invariance and neglecting scalar currents. Simultaneously the parity violating asymmetry parameter is determined to be γVA 1.08+0.46+0.14-0.41-0.25, consistent with the Standard Model prediction of γVA = 1 for left-handed tau neutrinos. Models of Kuehn and Santamaria and of Isgur et al. are used to fit distributions of the invariant 3π mass as well as 2π mass projections of the Dalitz plot. The model dependent mass and width of the a1 resonance are measured to be ma1 1.266 ± 0.014+0.012-0.002 GeV and Γa1 = 0.610 ± 0.049+0.053-0.019 GeV for the Kuehn and Santamaria model and ma1 = 1.202 ± 0.009+0.009-0.001 GeV and Γa1 = 0.422 ± 0.023+0.033-0.004 GeV for the Isgur et al. model. The model dependent values obtained for the parity violating asymmetry parameter are γVA = 0.87 ± 0.27+0.05-0.06 for the Kuehn and Santamaria model and γVA = 1.10 ± 0.31+0.13-0.14 for the Isgur et al. model. Within the Isgur et al. model the ratio of the S- and D-wave amplitudes is measured to be D/S = -0.09 ± 0.03 ± 0.01. (orig.)