Measurement of \Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-) and \Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)

TL;DR

This paper reports precise measurements of the electron-positron and muon-antimuon decay widths of the J/psi meson, improving the accuracy of its leptonic and total decay widths and testing lepton universality.

Contribution

The study provides new, more precise measurements of the J/psi meson's leptonic decay widths using data from the KEDR experiment, enhancing previous results.

Findings

Measured e*Br(J/psi->e+e-) and e*Br(J/psi->mu+mu-) with high precision.

Calculated the ratio e/mumu consistent with lepton universality.

Derived the leptonic width e and total width  of J/psi with improved accuracy.

Abstract

The products of the electron width of the J/\psi meson and the branching fraction of its decays to the lepton pairs were measured using data from the KEDR experiment at the VEPP-4M electron-positron collider. The results are \Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-)=(0.3323\pm0.0064\pm0.0048) keV, \Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)=(0.3318\pm0.0052\pm0.0063) keV. Their combinations \Gamma_{ee}\times(\Gamma_{ee}+\Gamma_{\mu\mu})/\Gamma=(0.6641\pm0.0082\pm0.0100) keV, \Gamma_{ee}/\Gamma_{\mu\mu}=1.002\pm0.021\pm0.013 can be used to improve theaccuracy of the leptonic and full widths and test leptonic universality. Assuming e\mu universality and using the world average value of the lepton branching fraction, we also determine the leptonic \Gamma_{ll}=5.59\pm0.12 keV and total \Gamma=94.1\pm2.7 keV widths of the J/\psi meson.