Measurement ofZdecays into lepton pairs

We present measurements by the Mark II experiment of the ratios of the leptonic partial widths of the Z boson to the hadronic partial width. The results are ${\mathrm{\Gamma }}_{\mathit{ee}}$/${\mathrm{\Gamma }}_{\mathrm{had}}$=0.${037}_{\mathrm{-}0.012}^{+0.016\mathrm{}}$, &=0.${053}_{\mathrm{-}0.015}^{0.020}$, and ${\mathrm{\Gamma }}_{\mathrm{\tau }\mathrm{\tau }}$/${\mathrm{\Gamma }}_{\mathrm{had}}$=0.${066}_{\mathrm{-}0.017}^{+0.021\mathrm{}}$, in good agreement with the standard-model prediction of 0.048. From the average leptonic width result, ${\mathrm{\Gamma }}_{\mathit{ll}}$/${\mathrm{\Gamma }}_{\mathrm{had}}$=0.${053}_{\mathrm{-}0.009}^{+0.010\mathrm{}}$, we derive ${\mathrm{\Gamma }}_{\mathrm{had}}$=1.${56}_{\mathrm{-}0.24}^{+0.28\mathrm{}}$ GeV. We find for the vector coupling constants of the tau and muon ${\mathit{v}}_{\mathrm{\tau }}^2$=0.31±0.${31}_{\mathrm{-}0.30}^{+0.43\mathrm{}}$ and ${\mathit{v}}_{\mathrm{\mu }}^2$=0.05±0.${30}_{\mathrm{-}0.23}^{+0.34\mathrm{}}$.