par Abreu, Pedro;Bertrand, Daniel 
;Bricman, Claude ; [et al.]
Référence Nuclear physics. B, 367, 3, page (511-574)
Publication Publié, 1991
;Bricman, Claude ; [et al.]Référence Nuclear physics. B, 367, 3, page (511-574)
Publication Publié, 1991
Article révisé par les pairs
| Résumé : | From measurements of the cross sections for e+e- → hadrons and the cross sections and forward-backward charge-asymmetries for e+e- → e+e-, μ+μu- and τ+τ- at several centreof-mass energies around the Za pole with the DELPHI apparatus, using approximately 150000 hadronic and leptonic events from 1989 and 1990, one determines the following Z0 parameters: the mass and total width MZ = 91.177 ± 0.022 GeV. ΓZ = 2.465 ± 0.020 GeV, the hadronic and leptonic partial widths Γh = 1.726 + 0.019 GeV, Γl = 83.4 ± 0.8 MeV, the invisible width Γinv = 488 ± 17 MeV, the ratio of hadronic over leptonic partial widths RZ = 20.70 + 0.29 and the Born level hadronic peak cross section σ0 = 41.84 ± 0.45 nh. A flavour-independent measurement of the leptonic cross section gives very consistent results to those presented above (Γl = 83.7 ± 0.8 MeV). From these results the number of light neutrino species is determined to be Nv, = 2.94 ± 0.10. The individual leptonic widths obtained are: Γe = 82.4 ± 1.2 MeV, Γμ = 86.9 ± 2.1 MeV and Γτ = 82.7±2.4 MeV. Assuming universality, the squared vector and axial-vector couplings of the Z0 to charged leptons are: V̄l 2 = 0.0003 ± 0.0010 and Āl 2 = 0.2508 ± 0.0027. These values correspond to the electroweak parameters: ρeff = 1.003 ± 0.011 and sin2θW eff = 0.241 ± 0.009. Within the Minimal Standard Model (MSM), the results can be expressed in terms of a single parameter: sin2θW MS = 0.2338 ± 0.0027. All these values are in good agreement with the predictions of the MSM. Fits yield 43 < mtop < 215 GeV at the 95% level. Finally, the measured values of ΓZ and Γinv are used to derive lower mass bounds for possible new particles. |
