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Measurement of electroweak parameters from Z decays into Fermion pairs

Research output: Contribution to journalJournal article


Journal publication date1990
JournalZeitschrift für Physik C Particles and Fields
Number of pages27
Original languageEnglish


We report on the properties of theZ resonance from 62 500Z decays into fermion pairs collected with the ALEPH detector at LEP, the Large Electron-Positron storage ring at CERN. We findM Z=(91.193±0.016exp±0.030LEP) GeV, Γ Z =(2497±31) MeV, σ had 0=(41.86±0.66)nb, and for the partial widths Γinv=(489±24) MeV, Γhad(1754±27) MeV, Γ ee =(85.0±1.6)MeV, Γ μμ =(80.0±2.5) MeV, and Γττ=(81.3±2.5) MeV, all in good agreement with the Standard Model. Assuming lepton universality and using a lepton sample without distinction of the final state we measure Γu=(84.3±1.3) MeV. The forward-backward asymmetry in leptonic decays is used to determine the vector and axial-vector weak coupling constants of leptors,g v 2(M Z 2)=(0.12±0.12)×10−2 andg A 2(M Z 2)=0.2528±0.0040. The number of light neutrino species isN ν=2.91±0.13; the electroweak mixing angle is sin2θW(M Z 2)=0.2291±0.0040.