Measurements of the decay of the Z0 into lepton pairs

Abstract We report on a measurement of the processes e+ e− → e+ e− , e+ e− → μ + μ − , and e+ e− → τ + τ − near the Z 0 pole. On the basis of 163 e+ e− , 101 μ + μ − and 87 τ + τ − events we obtain Γ ee =89±4±4 MeV, Γ μμ =85±9±6 MeV and Γ ττ =87±10±8 MeV, compatible with the standard model. Combining these with our previous results on hadronic Z 0 decays, we find a hadronic width Γ had =1787±81±90 MeV and an invisible width Γ inv =552±85±71 MeV.