Measurement of the Tau Polarisation at LEP

The polarisation of 's produced in Z decay is measured using 160 pb of data accumulated at LEP by the ALEPH detector between 1990 and 1995. The variation of the polarisation with polar angle yields the two parameters and which are consistent with the hypothesis of e- universality. Assuming universality, the value is obtained from which the effective weak mixing angle is derived. Received: 2 March 2001 / Published online: 8 June 2001