Polarized observables to probe Z′ at the e+e− linear collider

We study the sensitivity to the Z′ couplings of the processes e+e−→l+l−,b̄b and c̄c at the linear collider with s=500 GeV with initial beam polarization, for typical extended model examples. To this aim, we use suitable integrated, polarized, observables directly related to the helicity cross sections that carry information on the individual Z′ chiral couplings to fermions. We discuss the derivation of separate, model-independent limits on the couplings in the case of no observed indirect Z′ signal within the expected experimental accuracy. In the hypothesis that such signals were, indeed, observed we assess the expected accuracy on the numerical determination of such couplings and the consequent range of Z′ masses where the individual models can be distinguished from each other as the source of the effect.