Z0 effect in lepton-pair photoproduction

We study the modifications of lepton-pair photoproduction due to the spin-one Z⁰ appearing in gauge theories of the weak interactions. It gives rise to a resonance in the invariant mass of the pair. To obtain exact results we consider neutral currents involving only the known leptons, and still we find an effect significantly above the electromagnetic Bethe-Heitler background. Aside from the resonance, a unique parity-violating signal occurs in the form of an azimuthal asymmetry. For a typical Z⁰ mass of 10 GeV and beam energy of 400 GeV, it is on the order of 5%. Our results are easily adapted to any model of leptons and would probably be much increased by the hadronic part of the neutral current. The leptonic mechanism involves the VVA triangle, for which a previous result is extended to any energy, momentum transfer, and lepton mass.