Speaker
Xingyu Zhou
(IHEP Beijing)
Description
We measure the cross sections of $e^+e^- \to e^+e^-$ and $e^+e^- \to \mu^+\mu^-$ processes using the data set collected with the BESIII detector at fifteen energy points around the $J/\psi$ resonance. By fitting the theoretical cross section curves of the two processes as functions of energy to the measured cross section data simultaneously, the combinations of $J/\psi$ decay widths $\Gamma_{ee}\Gamma_{ee}/\Gamma_{\rm tot}$ and $\Gamma_{ee}\Gamma_{\mu\mu}/\Gamma_{\rm tot}$ are extracted to be ($0.348 \pm 0.008$) keV and ($0.339 \pm 0.005$) keV with a covariance $0.000,037$ keV$^2$.
With the fitting results, $\Gamma_{ee}/\Gamma_{\mu\mu}$ is evaluated as $1.025 \pm 0.014$, which proves the lepton universality. Assuming the lepton universality and combining the branching ratio of $J/\psi$ leptonic decay measured by BESIII in 2013, the total width $\Gamma_{\rm tot}$ and the leptonic width $\Gamma_{ll}$ are determined to be ($94.3 \pm 1.9$) keV and ($5.64 \pm 0.10$) keV, respectively.
Primary author
Xingyu Zhou
(IHEP Beijing)
