Using data acquired with the CLEO detector at the CESR $e^{+}{e}^{-}$ collider at $\sqrt{s}=3.773\mathrm{GeV}$, we measure the cross section for the radiative return process $e^{+}{e}^{-}\to \gamma J/\psi$, $J/\psi \to {\mu }^{+}{\mu }^{-}$, resulting in $\mathcal{B}(J/\psi \to {\mu }^{+}{\mu }^{-})\times {\Gamma }_{ee}(J/\psi )=0.3384\pm 0.0058\pm 0.0071\mathrm{keV}$, ${\Gamma }_{ee}(J/\psi )=5.68\pm 0.11\pm 0.13\mathrm{keV}$, and ${\Gamma }_{\mathrm{tot}}(J/\psi )=95.5\pm 2.4\pm 2.4\mathrm{keV}$, in which the errors are statistical and systematic, respectively. We also determine the ratio ${\Gamma }_{ee}[\psi (2S)]/{\Gamma }_{ee}(J/\psi )=0.45\pm 0.01\pm 0.02$.

• Received 16 December 2005

DOI:https://doi.org/10.1103/PhysRevD.73.051103