Measurement of the tau lepton polarisation at LEP2

A first measurement of the average polarisation Pτ of tau leptons produced in e+e− annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value Pτ=−0.164±0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV.