Measurement of the leptonic decay width of $J\mathrm{/}\psi$ using initial state radiation

Using a data set of 2.93 fb${}^{-1}$ taken at a center-of-mass energy of $\sqrt{s}$ = 3.773 GeV with the BESIII detector at the BEPCII collider, we measure the process $e^+e^-\rightarrow J/\psi\gamma\rightarrow \mu^+\mu^-\gamma$ and determine the product of the branching fraction and the electronic width $\mathcal B_{\mu\mu}\cdot \Gamma_{ee} = (333.4 \pm 2.5_{\rm stat} \pm 4.4_{\rm sys})$eV\mathrm{.}Usingtheearlier-publishedBESIIIresultfor$\mathcal B_{\mu\mu}$=(5.973$\pm$0.007${\rm stat}$ $\pm$ 0.037${\rm sys}$)\mathrm{\%},wederivethe$J/\psi$electronicwidth$\Gamma_{ee}$=(5.58$\pm$0.05$_{\rm stat}$ $\pm$ 0.08${}_{\mathrm{s}\mathrm{y}\mathrm{s}}$) keV.