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

TL;DR

This paper measures the leptonic decay width of the J/psi particle using initial state radiation at BESIII, providing a precise determination of its electronic width through analysis of e+e- collision data.

Contribution

The study presents a new measurement of the J/psi electronic width using initial state radiation, improving precision over previous results.

Findings

Measured the product of branching fraction and electronic width as (333.4 ± 2.5_stat ± 4.4_sys) eV.

Derived the J/psi electronic width as (5.58 ± 0.05_stat ± 0.08_sys) keV.

Utilized 2.93 fb^{-1} data at 3.773 GeV with BESIII detector.

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 $e^+e^-\rightarrow J/\psi\gamma\rightarrow \mu^+\mu^-\gamma$ 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. Using the earlier-published BESIII result for $\mathcal B_{\mu\mu}$ = (5.973 $\pm$ 0.007$_{\rm stat}$ $\pm$ 0.037$_{\rm sys}$)\%, we derive the $J/\psi$ electronic width $\Gamma_{ee}$~= (5.58 $\pm$ 0.05$_{\rm stat}$ $\pm$ 0.08$_{\rm sys}$) keV.