Measurement of<i>Z</i>decays into lepton pairs

Abstract

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 ${\mathrm{\ensuremath{\Gamma}}}_{\mathit{ee}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{had}}$=0.${037}_{\mathrm{\ensuremath{-}}0.012}^{+0.016}$, =0.${053}_{\mathrm{\ensuremath{-}}0.015}^{0.020}$, and ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{\ensuremath{\tau}}\mathrm{\ensuremath{\tau}}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{had}}$=0.${066}_{\mathrm{\ensuremath{-}}0.017}^{+0.021}$, in good agreement with the standard-model prediction of 0.048. From the average leptonic width result, ${\mathrm{\ensuremath{\Gamma}}}_{\mathit{ll}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{had}}$=0.${053}_{\mathrm{\ensuremath{-}}0.009}^{+0.010}$, we derive ${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{had}}$=1.${56}_{\mathrm{\ensuremath{-}}0.24}^{+0.28}$ GeV. We find for the vector coupling constants of the tau and muon ${\mathit{v}}_{\mathrm{\ensuremath{\tau}}}^{2}$=0.31\ifmmode\pm\else\textpm\fi{}0.${31}_{\mathrm{\ensuremath{-}}0.30}^{+0.43}$ and ${\mathit{v}}_{\mathrm{\ensuremath{\mu}}}^{2}$=0.05\ifmmode\pm\else\textpm\fi{}0.${30}_{\mathrm{\ensuremath{-}}0.23}^{+0.34}$.