Measurement of the Z resonance parameters at LEP

Abstract. The properties of the Z resonance are measured from the analysis of 4.5 million Z decays into fermion pairs collected with the Aleph detector at LEP. The data are consistent with lepton universality. The resonance parameters are measured to be , GeV, nb and, combining the three lepton flavours, . The corresponding number of light neutrino species is and the strong coupling constant is . The lepton pair forward-backward asymmetry is measured to be from which the effective weak mixing angle is derived: . The measurement of the leptonic width MeV leads to a determination of the effective parameter . The data support the Standard Model and favour a light Higgs. Received: 16 July 1999 / Published online: 17 March 2000