MODEL INDEPENDENT FITTING TO THE Z-LINE SHAPE

An improved model independent formula to fit the Z line shape parameters is presented. The accuracy of the QED radiative corrections used in the formula is estimated, as is the absolute accuracy of the formula itself. The precision of the formula is compared with existing fitting formulae, in terms of cross sections produced and in terms of the Z parameters returned from a fit. The errors which the LEP-SLC experiments can expect to achieve on the Z parameters are examined as a function of total integrated luminosity. The formula presented here can fit the Z parameters with high accuracy: below 1 MeV for the Z mass, the order of 1 MeV for total width, and below 0.04% for the hadronic and leptonic peak cross sections. Such biases will remain much below the expected experimental uncertainties from LEP and SLC.