Measurement of the leptonic decay width of $J/\ddot{I}ˆ$ using initial state radiation

Abstract

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 $e^{+}{e}^{-}\to J/\ddot{I}ˆ{\hat{I}}^3\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}{\hat{I}}^3$ and determine the product of the branching fraction and the electronic width ${\mathcal{B}}_{\hat{I}¼\hat{I}¼}\cdot \hat{I}{“}_{ee}=(333.4\pm 2.5_{\mathrm{stat}}\pm 4.4_{\mathrm{sys}})$~eV. Using the earlier-published BESIII result for ${\mathcal{B}}_{\hat{I}¼\hat{I}¼}$ = (5.973 $\pm$ 0.007${}_{\mathrm{stat}}$ $\pm$ 0.037${}_{\mathrm{sys}}$)\%, we derive the $J/\ddot{I}ˆ$ electronic width $\hat{I}{“}_{ee}$~= (5.58 $\pm$ 0.05${}_{\mathrm{stat}}$ $\pm$ 0.08${}_{\mathrm{sys}}$) keV.

8 pages, 2 figures