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

The ratio of the electron and muon widths of the J/ψJ/ψ meson has been measured using direct J/ψJ/ψ decays in the KEDR experiment at the VEPP-4M electron–positron collider. The resultΓe+e−(J/ψ)/Γμ+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/ψJ/ψ lepton width determination with up to 1% accuracy.