Z-PRODUCTION CROSS-SECTIONS AND LEPTON PAIR FORWARD-BACKWARD ASYMMETRIES

Precise values of the Z resonance cross sections and lepton pair forward-backward asymmetries are measured from a sample of 1.3 million Z decays into hadrons and charged leptons taken with the ALEPH detector at LEP. A silicon-tungsten luminosity calorimeter was installed in ALEPH in 1992, permitting the determination of the absolute luminosity to a systematic precision of 0.15% (experimental) and 0.25% (theoretical). This is combined with a better understanding of the hadronic event selection and an improved tau pair selection. Including the ALEPH results of the past three years one obtains sigma(h)0 = (41.60 +/- 0.16) nb, and R(l) = 20.69 +/- 0.09. The corresponding number of light neutrino species is N(v) = 2.983 +/- 0.034. The lepton pair forward-backward' asymmetry is used to derive the ratio of vector to axial-vector couplings of leptons: g(V)2(M(Z)2)/g(A)2(M(Z)2) = 0.0058 +/- 0.0011. An application of these results to constrain one model with extra Z bosons is presented.