Test of CP-invariance in e+e−→Z0→τ+τ− and a limit on the weak dipole moment of the τ lepton

Abstract Using a sample of 5558 Z 0 → τ + τ − decays produced at LEP a direct test of CP -invariance in the neutral current reaction e + e − → τ + τ − is performed. Samples of events where eachy τ decays into a single particle have been isolated for the construction of CP -odd observables. Three different event classes are considered: lepton-lepton, lepton-hadron, and hadron-hadron. No evidence for a non-zero expectation value of the considered CP -observables and hence for CP -violation is observed. Quantitatively, we deduce from this null result an estimate on the weak dipole moment d τ (m 2 Z = (−4.5 ± 5.3 ± 1.4) × 10 −17 e cm for the lepton-lepton signature and d τ (m 2 Z = (1.4 ± 3.7 ± 1.3) × 10 −17 e cm for the hadron-hadron signature. Combining these results we place a limit with 95% confidence of | d τ |⩽7.0 × 10 −17 e cm.