A test of higher order electroweak theory in Z0 decays to two leptons with an associated pair of charged particles

The OPAL detector at LEP was used to study the reactions e+e-→e+e-V, e+e-→μ+μ-V and e+e-→τ+τ-V, where V represents an additional pair of oppositely charged tracks coming directly from the event vertex. Rates for these processes were determined using selection criteria similar to those described in a recent publication by the ALEPH Collaboration in which a possible excess in the τ+τ-V channel was reported. In the OPAL data no discrepancy was found between the measured production rates and those expected from known physics processes in any of the three channels. The measured distributions of the invariant mass of the V and angle between the V and closest lepton are also described adequately within the context of the standard model. (orig.)