Hadronic decay structure and ν τ helicity in τ - → π - π -π +ν τ with the OPAL Detector at LEP

The hadronic structure of τ ^- → π ^-π ^-π ⁺ν _τ events observed with the OPAL detector at LEP during 1992-1994 has been measured. A model dependent as well as a model independent approach have been used. Deficiencies of the two theoretical models considered become visible with the available data sample. A non-resonant contribution seems to be required in the model description. Interference terms of axial-vector and non-axial-vector contributions have been measured for the first time in a model independent approach. No evidence for non-axial-vector contributions has been found. Finally, the parity violating asymmetry parameter γ _VA has been measured model independently to be 1.29 ± 0.26 ± 0.11 and, for comparison, it has also been measured in a model dependent way.