Measurement of J/psi leptonic width with the KEDR detector
  We report a new precise determination of the leptonic widths of the J/psi meson performed with the KEDR detector at the VEPP-4M $e^{+}e^{-}$ collider. The measured values of the J/psi parameters are: \Gamma_{ee}\times\Gamma_{ee}/\Gamma = 0.3323 \pm 0.0064 (stat.) \pm 0.0048 (syst.) keV \Gamma_{ee}\times\Gamma_{\mu\mu}/\Gamma=0.3318 \pm 0.0052 (stat.) \pm 0.0063 (syst.) keV. Assuming $e\mu$ universality and using the table value of the branching ratios the leptonic \Gamma_{ll}= 5.59 \pm 0.12 keV width and the total \Gamma=94.1 \pm 2.7 keV widths were obtained. We also discuss in detail a method to calculate radiative corrections at a narrow resonance. 
V.V.Anashin, V.M.Aulchenko, E.M.Baldin, A.K.Barladyan, A.Yu.Barnyakov,   M.Yu.Barnyakov, S.E.Baru, I.Yu.Basok, O.L.Beloborod...
hep-ex