An upper limit on the anomalous magnetic moment of the τ lepton

Abstract

Using radiative Z 0→ τ +τ −γ events collected with the OPAL detector at LEP at s =M Z during 1990–95, a direct study of the electromagnetic current at the τγ vertex has been performed in terms of the anomalous magnetic form factor F 2 of the τ lepton. The analysis is based on a data sample of 1429 e +e − →τ +τ −γ events which are examined for a deviation from the expectation with F 2=0. From the non-observation of anomalous τ +τ −γ production a limit of −0.068<F 2<0.065 is obtained. This can also be interpreted as a limit on the electric dipole form factor F 3 as |eF 3|<3.7×10 −16 e cm . The above ranges are valid at the 95% confidence level.