Testing for heavier vector bosons in e +e − at Z peak. A comparative study of different models

Abstract

We have analyzed the experimental consequences which the existence of a heavy neutral gauge vector boson may produce in e +e − measurements made at energies around the Z mass. The analysis has been made as model independent as possible and it is mainly based upon the classification of the various models according to the transformation properties of the extra neutral gauge field under U(1) em. As specific examples we consider extra U(1) and left-right (LR) models, as well as a model with electroweak symmetry broken by a strongly interacting sector (BESS). For the analysis we have used the new data from CDF, UA2 and SLC/LEP1 on W and Z masses. We give analytical expressions for the deviations from the standard model (SM) of the observables relevant at LSC/LEP1 energies, such as widths and asymmetries. The range of the allowed deviations from the SM is explicitly evaluated for each of the models discussed. Small deviations are generally expected in the Z line-shape parameters; for extra U(1) and LR models the most sensitive observables are the leptonic peak cross section and width. Potentially large effects might show up in asymmetry measurements with a pattern distinguishing BESS from the other models. Larger deviations are favoured in BESS by a larger top mass and the contrary holds for the other models.