An S matrix analysis of the Z resonance

Abstract The S matrix ansatz is a rigorously model independent approach to describe the cross-sections and asymetries in e + e − annihilation. Using the cross-sections and asymetries measured with the L3 detector during the 1990 and 1991 running period, we determine the mass and the width of the Z boson, the contributions of the Z exchange and the γZ interference. Including the polarization of the τ lepton in the analysis, the leptonic helicity amplitudes of the scattering process are determined assuming lepton universality. The results are compared with other model independent ansatzes as realized in ZFITTER. A systematic bias of the Z mass due to the γZ interference term is detected, which leads to an underestimation of the error on m Z for model independent determinations.