Universal and nonuniversal new physics effects in a general four-fermion process: AZ-peak subtracted approach

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Abstract
We calculate, using a Z-peak subtracted representation of four-fermion processes previously illustrated for the case of electron-positron annihilation into charged lepton-antilepton pairs, the corresponding expressions of the new physics contributions for the case of final quark-antiquark states, allowing the possibility of both universal and nonuniversal effects. We show that, in each case, the main result obtained for the final lepton channel can be generalized, so that every experimentally measurable quantity can be expressed in terms of input parameters measured on the Z resonance, of α(0) and of a small number of subtracted one loop expressions. Some examples of models are considered for several c.m. energy values, showing that remarkable simplifications are often introduced by our approach. In particular, for the case of a dimension-six Lagrangian with anomalous gauge couplings, the same reduced numer of parameters that would affect the observables of final leptonic states are essentially retained when one moves to final hadronic states. This leads to great simplifications in the elaboration of constraints and, as a gratifying by-product, to the possibility of making the signal from these models clearly distinguishable from those from other (both universal and nonuniversal) competitors. © 1996 The American Physical Society.