Precise determination of the Z resonance parameters at LEP: ''Zedometry''

This final analysis of hadronic and leptonic cross-sections and of leptonic forward-backward asymmetries in e+e- collisions with the OPAL detector makes use of the full LEP 1 data sample comprising 161 pb-1 of integrated luminosity and 4.5 x 106 selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from γ/Z interference allows the parameters of the Z resonance to be determined in a model-independent way. Our results are in good agreement with lepton universality and consistent with the vector and axial-vector couplings predicted in the Standard Model. A fit to the complete dataset yields the fundamental Z resonance parameters: mZ=(91.1852 ±0.0030) GeV, ΓZ=(2.4948 ±0.0041) GeV, σ0h=(41.501 ±0.055) nb, Rl=20.823 ±0.044, and AFB0,l=0.0145 ±0.0017. Transforming these parameters gives a measurement of the ratio between the decay width into invisible particles and the width to a single species of charged lepton, Γinv/Γll=5.942 ±0.027. Attributing the entire invisible width to neutrino decays and assuming the Standard Model couplings for neutrinos, this translates into a measurement of the effective number of light neutrino species, Nν=2.984 ±0.013. Interpreting the data within the context of the Standard Model allows the mass of the top quark, mt=(162 +29-16) GeV, to be determined through its influence on radiative corrections. Alternatively, utilising the direct external measurement of mt as an additional constraint leads to a measurement of the strong coupling constant and the mass of the Higgs boson: αs(mZ)=0.127 ±0.005 and mH=(390+750-280) GeV. (orig.)