The ALEPH Collaboration : Search for anomalous weak dipole moments of the τ lepton

The anomalous weak dipole moments of the τ lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155 pb−1. Tau leptons produced in the reaction e+e− → τ+τ− at energies close to the Z mass are studied using their semileptonic decays to π, ρ, a1 → π2π or a1 → 3π. The real and imaginary components of both the anomalous weak magnetic dipole The ALEPH Collaboration: Search for anomalous weak dipole moments of the τ lepton 293 moment and the CP-violating anomalous weak electric dipole moment, Re μτ , Im μτ , Re dτ and Im dτ , are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95% CL): |Re μτ | < 1.14 × 10−3, |Im μτ | < 2.65 × 10−3, |Re dτ | < 0.91 × 10−3, and |Im dτ | < 2.01 × 10−3.