Measurement of the ratio of the lepton widths Γee/Γμμ for the J/ψ meson

Abstract The ratio of the electron and muon widths of the J / ψ meson has been measured using direct J / ψ decays in the KEDR experiment at the VEPP-4M electron–positron collider. The result Γ e + e − ( J / ψ ) / Γ μ + μ − ( J / ψ ) = 1.0022 ± 0.0044 ± 0.0048 ( 0.65 % ) is in good agreement with the lepton universality. The experience collected during this analysis will be used for J / ψ lepton width determination with up to 1% accuracy.