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The cross sections for e + e - → hadrons, e + e - , μ + μ - have been measured in the vicinity of the J/ψ resonance using the BES detector operated at BEPC. The partial widths for J/ψ to hadrons, electrons, muons and the total width have been determined to be Γ h = 74.1 ± 8.1 keV, Γ e = 5.14 ± 0.39 keV, Γ μ = 5.13 ± 0.52 keV,...