Testing the standard model versus left-right models on and off theZresonance

We examine the high-energy predictions of left-right models which are consistent with constraints from low-energy data. These are compared to the predictions of the standard electroweak gauge model to determine how well the theories can be distinguished by measurements in this mass region of the standard $Z$ boson resonance. We find a nontrivial class of left-right models in which the lowest-mass $Z$ is indistinguishable in mass and fermion couplings from the standard $Z$, but which allow a second $Z$ boson as low as 200 GeV. We discuss the sensitivity of the lower limit on the second-$Z$ mass to the results of the atomic parity-violation measurement and find that the newest data relaxes the mass limit in a general left-right model to $M_{Z_2}\ge 150$ GeV.