Measurement of Γee×Bμμ for ψ(2S) meson

Abstract The product of the electronic width of the ψ (2S) meson and the branching fraction of its decay to the muon pair was measured in the e + e − → ψ (2S) → μ + μ − 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: Γ e e × B μ μ = 19.3 ± 0.3 ± 0.5 eV . Adding the previous KEDR results on hadronic and leptonic channels, the values of the ψ (2S) electronic width were obtained under two assumptions: either with the assumption of lepton universality Γ e e = 2.279 ± 0.015 ± 0.042 keV or without it, summing up hadronic and three independent leptonic channels Γ e e = 2.282 ± 0.015 ± 0.042 keV .