Polarisation measurement using leptonic τ decays

A precision measurement of τ polarisation at LEP tests neutral couplings of τ leptons providing therefore a stringent test of the Standard Model predictions. The polarisation measurement using leptonic τ decays which constitute an important part of this analysis is discussed with a special emphasis on the analysis of the systematic errors. This measurement is based on approximately 600 000 Z → τ+τ- decays collected by the four LEP experiments during the 1990-1994 running periods. (orig.)