Measurement of $\Gamma_{ee}\times\mathcal{B}_{\mu\mu}$ for $\psi(2S)$ meson

TL;DR

This paper reports a precise measurement of the product of the electronic width and muonic branching fraction of the $ ext{psi}(2S)$ meson, refining its electronic width with new data and analysis assumptions.

Contribution

The study provides a new measurement of $ ext{Gamma}_{ee} imes ext{B}_{}$ for $ ext{psi}(2S)$ and refines the electronic width using combined data and assumptions of lepton universality.

Findings

Measured $ ext{Gamma}_{ee} imes ext{B}_{}$ as 19.3 eV with uncertainties.

Derived $ ext{Gamma}_{ee}$ as approximately 2.28 keV under different assumptions.

Improved precision of $ ext{psi}(2S)$ electronic width measurements.

Abstract

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: \[ \Gamma_{ee} = 2.282 \pm 0.015 \pm 0.042 ~\text{keV}. \]