Measurement of the ratio of the leptonic widths $Gamma_{ee}/Gamma_{mumu}$ for the $J/psi$ meson

The ratio of the electron and muon widths of the $J/psi$ meson has been measured using direct $J/psi$ decays in the KEDR experiment at the VEPP-4M electron-positron collider. The result $Gamma_{ee}(J/psi)/Gamma_{mumu}(J/psi)=1.0022pm0.0044pm0.0048 (0.65%)$ is in good agreement with the lepton universality. The experience collected during this analysis will be used for a $J/psi$ lepton width determination with up to 1% accuracy.