Measurement of the Z resonance parameters at LEP

R. Barate, D. Decamp, P. Ghez, C. Goy, J. P. Lees, A. Lucotte, E. Merle, M. N. Minard, B. Pietrzyk, R. Alemany, M. P. Casado, M. Chmeissani, P. Comas, J. M. Crespo, E. Fernandez, M. Fernandez-Bosman, L. Garrido, E. Graugès, A. Juste, M. MartinezG. Merino, R. Miquel, L. M. Mir, S. Orteu, A. Pacheco, I. C. Park, J. Perlas, I. Riu, F. Sanchez, A. Colaleo, D. Creanza, M. de Palma, G. Iaselli, G. Maggi, M. Maggi, S. Nuzzo, A. Ranieri, G. Raso, F. Ruggieri, G. Selvaggi, L. Silvestris, P. Tempesta, A. Tricomi, G. Zito, X. Huang, J. Lin, Q. Ouyang, T. Wang, Y. Xie, R. Xu, S. Xue, J. Zhang, L. Zhang, W. Zhao, D. Abbaneo, A. Bazarko, U. Becker, E. Blucher, G. Bonvicini, P. Bright-Thomas, M. Cattaneo, F. Cerutti, V. Ciulli, G. Dissertori, H. Drevermann, R. W. Forty, M. Frank, T. C. Greening, R. Hagelberg, A. W. Halley, J. B. Hansen, J. Harvey, R. Jacobsen, P. Janot, B. Jost, J. Knobloch, P. Lazeyras, I. Lehraus, P. Maley, P. Mato, J. May, A. Moutoussi, F. Ranjard, L. Rolandi, D. Schlatter, M. Schmitt, O. Schneider, P. Spagnolo, W. Tejessy, F. Teubert, I. R. Tomalin, E. Tournefier, R. Veenhof, W. Wiedenmann, A. E. Wright, Z. Ajaltouni, F. Badaud, G. Chazelle, O. Deschamps, A. Falvard

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The properties of the Z resonance are measured from the analysis of 4.5 million Z decays into fermion pairs collected with the ALEPH detector at LEP. The data arc consistent with lepton universality. The resonance parameters are measured to be MZ = (91.1885 ± 0.0031) GeV/c2, ΓZ = (2.4951 ± 0.0043) GeV. σ0had = (41.559 ± 0.058) nb and, combining the three lepton flavours, Rℓ = 20.725 ± 0.039. The corresponding number of light neutrino species is Nv = 2.983± 0.013 and the strong coupling constant is αs (MZ) = 0.114±0.004±0.002QCD + 0.005 log10 [MH/150 GeV/c2]. The lepton pair forward-backward asymmetry is measured to be A0,ℓFB = 0.0173 ± 0.0016 from which the effective weak mixing angle is derived: sin2 θlepteff = 0.23089 ± 0.00089. The measurement of the leptonic width Γℓℓ = 84.02 ± 0.15 MeV leads to a determination of the effective ρ parameter ρlepteff = 1.0064 ± 0.0018. The data support the Standard Model and favour a light Higgs.
Original languageEnglish
Pages (from-to)1-50
JournalEuropean Physical Journal C
Issue number1
Publication statusPublished - 1 Jan 2000


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