Pion and Kaon Pair Production in Photon-Photon Collisions

We report measurements of the two-photon processes $e^{+}{e}^{-}\to e^{+}{e}^{-}{\pi }^{+}{\pi }^{-}$ and $e^{+}{e}^{-}\to e^{+}{e}^{-}{K}^{+}{K}^{-}$, at an $e^{+}{e}^{-}$ center-of-mass energy of 29 GeV. In the ${\pi }^{+}{\pi }^{-}$ data a high-statistics analysis of the $f\left(1270\right)\mathrm{}$ results in a $\gamma \gamma$ width $\Gamma (\gamma \gamma \to f)=3.2\mathrm{}\pm 0.4$ keV. The ${\pi }^{+}{\pi }^{-}$ continuum below the $f$ mass is well described by a QED Born approximation, whereas above the $f$ mass it is consistent with a QCD-model calculation if a large contribution from the $f$ is assumed. For the $K^{+}{K}^{-}$ data we find agreement of the high-mass continuum with the QCD prediction; limits on $f^{\prime }\mathrm{}\left(1520\right)\mathrm{}$ and $\theta \mathrm{}\left(1720\right)\mathrm{}$ formation are presented.