The product of the electronic width of the $\psi(2S)$ meson and the branching fraction of its decay to the muon pair was measured in the $e^{ +}e^{ -} \to \psi(2S) \to \mu^{ +}\mu^{ -}$ process using nine data sets corresponding to an integrated luminosity of about 6.5 pb$^{ -1}$ collected with the KEDR detector at the VEPP-4M electron-positron collider: \[ \Gamma_{ ee}\times\mathcal{ B}_{ \mu\mu} = 19.3 \pm 0.3 \pm 0.5 ~\text{ eV}. \] Adding the previous KEDR results on hadronic and leptonic channels, the values of the $\psi(2S)$ electronic width were obtained under two assumptions: either with the assumption of lepton universality \[ \Gamma_{ ee} = 2.279 \pm 0.015 \pm 0.042 ~\text{ keV} \] or without it, summing up hadronic and three independent leptonic channels: \[ \Gamma_{ ee} = 2.282 \pm 0.015 \pm 0.042 ~\text{ keV}. \]
Categories: hep-ex