The Tau weak-magnetic dipole-moment

We calculate the prediction for the anomalous weak-magnetic form factor of the tau lepton at q2=M2Z within the Standard Model. With all particles on-shell, this is a electroweak gauge invariant quantity. Its value is awτ(M2Z)=−(2.10+0.61i)×10−6. We show that the transverse and normal components of the single-tau polarization of tau pairs produced at e+e− unpolarized collisions are sensitive to the real and absorptive parts of the anomalous weak-magnetic dipole moment of the tau. The sensitivity one can achieve at LEP in the measurement of this dipole moment is discussed