Study of the $e^{+}{e}^{-}\to K^{+}{K}^{-}$ reaction in the energy range from 2.6 to 8.0 GeV

Abstract

The $e^{+}{e}^{-}\to K^{+}{K}^{-}$ cross section and charged-kaon electromagnetic form factor are measured in the $e^{+}{e}^{-}$ center-of-mass energy range ($E$) from 2.6 to 8.0 GeV using the initial-state radiation technique with an undetected photon. The study is performed using 469 fb${}^{-1}$ of data collected with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ collider at center-of-mass energies near 10.6 GeV. The form factor is found to decrease with energy faster than $1/E^2$, and approaches the asymptotic QCD prediction. Production of the $K^{+}{K}^{-}$ final state through the $J/\psi$ and $\psi (2S)$ intermediate states is observed. The results for the kaon form factor are used together with data from other experiments to perform a model-independent determination of the relative phases between single-photon and strong amplitudes in $J/\psi$ and $\psi (2S)\to K^{+}{K}^{-}$ decays. The values of the branching fractions measured in the reaction $e^{+}{e}^{-}\to K^{+}{K}^{-}$ are shifted relative to their true values due to interference between resonant and nonresonant amplitudes. The values of these shifts are determined to be about $\pm 5\%$ for the $J/\psi$ meson and $\pm 15\%$ for the $\psi (2S)$ meson.

18 pages, 19 postscript figures