Measurement of J/psi leptonic width with the KEDR detector

TL;DR

This paper presents a precise measurement of the leptonic widths of the J/psi meson using the KEDR detector, providing updated parameters and discussing radiative correction methods.

Contribution

The study introduces a new precise determination of J/psi leptonic widths and details a method for calculating radiative corrections at narrow resonances.

Findings

Measured a_{ee} imesa_{ee}/a = 0.3323 b1 0.0064 (stat.) b1 0.0048 (syst.) keV

Measured a_{ee} imesa_{\u03bca}/a = 0.3318 b1 0.0052 (stat.) b1 0.0063 (syst.) keV

Calculated a_{ll} = 5.59 b1 0.12 keV and a = 94.1 b1 2.7 keV

Abstract

We report a new precise determination of the leptonic widths of the J/psi meson performed with the KEDR detector at the VEPP-4M $e^{+}e^{-}$ collider. The measured values of the J/psi parameters are: \Gamma_{ee}\times\Gamma_{ee}/\Gamma = 0.3323 \pm 0.0064 (stat.) \pm 0.0048 (syst.) keV \Gamma_{ee}\times\Gamma_{\mu\mu}/\Gamma=0.3318 \pm 0.0052 (stat.) \pm 0.0063 (syst.) keV. Assuming $e\mu$ universality and using the table value of the branching ratios the leptonic \Gamma_{ll}= 5.59 \pm 0.12 keV width and the total \Gamma=94.1 \pm 2.7 keV widths were obtained. We also discuss in detail a method to calculate radiative corrections at a narrow resonance.