Special features of Z couplings to fermions and new physics detection

Abstract

We consider a number of observable Z couplings to fermions that will be measured in the very near future in the first phase (no polarization, E<110 GeV, luminosity <10 31) of LEP 100. We show that the effect on these quantities of a large number of models predicting a new vector boson Z′ is such that one can generate couples of linear combinations of the couplings (and of the W Z mass ratio) in whose plane several models (with at least two free parameters) remain simply associated to a straight line. This allows us to establish a correspondence between points of some plane of experimental variables and models that might lead to a complete identification of the latter ones or, in the most pessimistic case, to new and much stricter bounds on their parameters.