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

Abbiendi, G; Ainsley, C; Åkesson, PF; Alexander, G; Allison, J; Anagnostou, G; Anderson, KJ; ... Hanson, GG; + view all (2001) Precise determination of the Z resonance parameters at LEP: "Zedometry". European Physical Journal C , 19 (4) pp. 587-651. Green open access

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Abstract

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 161pb-1 of integrated luminosity and 4.5 × 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 A0,ℓFB = 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, Nv = 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.

Type: Article
Title: Precise determination of the Z resonance parameters at LEP: "Zedometry"
Open access status: An open access version is available from UCL Discovery
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/9837
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