Eur. Phys. J. C 19, 587-651
Precise determination of the Z resonance parameters at LEP: "Zedometry"The OPAL Collaboration
G. Abbiendi and et al.
Dipartimento di Fisica dell' Università di Bologna and INFN, 40126 Bologna, Italy
(Received: 1 December 2000 / Published online: 6 April 2001 -© Springer-Verlag 2001)
This final analysis of hadronic and leptonic cross-sec tions and of leptonic forward-backward asymmetries in e+e- collisions with the OPAL detector makes use of the full LEP1 data sample comprising 161 pb-1 of integrated luminosity and selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from 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: , , , , and . 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, . 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, . 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: and mH = (390+750-280) GeV.
© Società Italiana di Fisica, Springer-Verlag 2001