DIFFERENTIATING VARIOUS EXTRA Z'S AT FUTURE COLLIDERS

We propose a way to differentiate between various extra U(1) models us ing flavor tagging in the decay modes Z' --> qqBAR once the extra Z' i s observed at future colliders in the lepton channel. A generalization of the R parameter, namely, one for charge 1/3 and one for charge 2/3 quark gives a two-parameter test for the various models. Flavor taggi ng eliminates the uncertainty because of extra fermions and can reduce the QCD background at SSC/LHC dramatically. For E6 and SO(10) based m odels the former is always 3. This seems to be a very good way to elim inate certain models.