Pion and Kaon Pair Production in Photon-Photon Collisions

We report measurements of the two-photon processes ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{K}^{+}{K}^{\ensuremath{-}}$, at an ${e}^{+}{e}^{\ensuremath{-}}$ center-of-mass energy of 29 GeV. In the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ data a high-statistics analysis of the $f(1270)$ results in a $\ensuremath{\gamma}\ensuremath{\gamma}$ width $\ensuremath{\Gamma}(\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}f)=3.2\ifmmode\pm\else\textpm\fi{}0.4$ keV. The ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ 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 ${K}^{+}{K}^{\ensuremath{-}}$ data we find agreement of the high-mass continuum with the QCD prediction; limits on ${f}^{\ensuremath{'}}(1520)$ and $\ensuremath{\theta}(1720)$ formation are presented.