Search for CP Violation in the Decay Z → Τ+τ−

Data collected by ALEPH in the years 1990, 1991 and 1992 have been used to update a previous search for CP violation in the decay of the Z into τ+τ−. The measurement of the weak dipole form factor of the τ lepton has been performed by studying correlations between the τ leptons. No signal of CP violation was found. The weak dipole form factor is found to be d̃τ = (+0.15 ± 0.58stat ± 0.38sys)10−17e · cm, obtained with 19628 identified τ+τ− events. This gives an upper limit on the weak dipole form factor of d̃τ < 1.5 · 10−17 e · cm at the 95% confidence level.