STUDY OF THE LEPTONIC DECAYS OF THE Z0 BOSON

Measurements are presented of the cross section ratios Rℓ= σℓ(e+e-→ℓ+ ℓ-) σh(e for ℓ=e, μ and τ using data taken from a scan around the Z0. The results are Re=(5.09±o.32±0.18)%, Rμ=(0.46±0.35±0.17)% and Rτ=(4.72±0.38±0.29)% where, for the ratio Re, the t-channel contribution has been subtracted. These results are consistent with the hypothesis of lepton universality and test this hypothesis at the energy scale s∼8300 GeV2. The absolute cross sections σℓ(e+e-→ℓ+ ℓ-) have also been measured. From the cross sections the leptonic partial widths Γe=(83.2±3.0±2.4) MeV, (ΓeΓμ) 1 2=(84.6±3.0±2.4) MeV and (ΓeΓτ) 1 2=(82.6±3.3±3.2) MeV have been extracted. Assuming lepton universality the ratio Γℓ Γh=(4.89±0.20±0.12) × 10-2 w was obtained, together with Γℓ=(83.6±1.8±2.2) MeV. The number of light neutrino species is determined to be Nv=3.12±0.24±0.25. Al the data are consistent with the predictions of the standard model. © 1990.