Search for CP violation in the decay Z → τ+τ−

Abstract

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 d ̃ τ = (+0.15 ± 0.58 stat ± 0.38 sys )10 −17e · cm, obtained with 19628 identified τ + τ − events. This gives an upper limit on the weak dipole form factor of d ̃ τ < 1.5 · 10 −17 e · cm at the 95% confidence level.