Z′ interference effects from TRISTAN to LEP2

We discuss the potential of present e+e− colliders to probe for a heavy Z′ boson via its interference effects, in a model-independent framework. The leptonic channel is unambiguous, and thus favourable over the hadronic ones. The effects on the leptonic cross section σμμ and the forward-backward difference σFB, induced by a heavy Z′ with arbitrary couplings, are uniquely determined at LEP2 energies. It results in negative deviations from the standard model predictions, due to destructive γ - Z′ and Z - Z′ interferences. This distinctive property could be useful in discriminating Z′ effects from other new physics signals. Comparison of the e+e− collider potentials indicates that already after one year of operation, LEP2 will achieve a sensitivity to Z′ that exceeds the current one at TRISTAN.