Measurement of $\hat{I}{“}_{ee}\times {\mathcal{B}}_{\hat{I}¼\hat{I}¼}$ for $\ddot{I}ˆ(2S)$ meson

Abstract

The product of the electronic width of the $\ddot{I}ˆ(2S)$ meson and the branching fraction of its decay to the muon pair was measured in the $e^{+}{e}^{-}\to \ddot{I}ˆ(2S)\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ 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: \[ Γ_{ee}\times\mathcal{B}_{μμ} = 19.3 \pm 0.3 \pm 0.5 ~\text{eV}. \] Adding the previous KEDR results on hadronic and leptonic channels, the values of the $\ddot{I}ˆ(2S)$ electronic width were obtained under two assumptions: either with the assumption of lepton universality \[ Γ_{ee} = 2.279 \pm 0.015 \pm 0.042 ~\text{keV} \] or without it, summing up hadronic and three independent leptonic channels: \[ Γ_{ee} = 2.282 \pm 0.015 \pm 0.042 ~\text{keV}. \]