Phenomenology of an extra neutral gauge boson in electron-positron collisions

Models with an extra neutral gauge boson (Z’) are discussed. We review present limits on the properties of such a Z’ which follow from requiring that the $Z^0$ mass not be shifted excessively through mixing, from neutral-current experiments, and from the structure of the mass matrix which follows from the Higgs-boson content of particular theories. We then examine what extensions in sensitivity can come from electron-positron annihilation experiments at the Z peak, with emphasis on the importance of cross-section measurements for final states involving lepton or quark pairs, followed by asymmetry measurements with polarized beams. Finally, we consider the additional information provided by asymmetry measurements in electron-positron collisions at energies above the Z.