Hunting new vector bosons in high precision measurements without polarization

We illustrate a strategy to identify the effect of a possible extra neutral vector boson of several different theoretical origins (extended gauge groups, composite models, models with a strongly interacting Higgs sector), assuming that only precision experiments without polarized e+e- beams were avaialble. We show that it might be relatively easy to discover evidence of genuine New Physics (i.e., effects not depending on the value of the top mass, or on the existence of new families...) if a certain set of observables, including the final τ polarization in unpolarized e+e- annihilation, were measured. The region of possible confusion between different theoretical models would be, though, sensibly larger than in the case in which e+e- polarization were available. (orig.)