Exclusive production ofpp¯π+π−in photon-photon collisions

We report a measurement of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}p\overline{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ process with the TPC/Two-Gamma facility at the PEP ${e}^{+}{e}^{\ensuremath{-}}$ storage ring at SLAC. Forty-five $p\overline{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ events were identified in data corresponding to an integrated ${e}^{+}{e}^{\ensuremath{-}}$ luminosity of 142 ${\mathrm{pb}}^{\ensuremath{-}1}$. The cross section for $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}p\overline{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ is given both as a function of the $\ensuremath{\gamma}\ensuremath{\gamma}$ center-of-mass energy ${W}_{\ensuremath{\gamma}\ensuremath{\gamma}}$, with ${W}_{\ensuremath{\gamma}\ensuremath{\gamma}}$ between 2.5 and 5.5 GeV, and as a function of the in variant mass squared ${q}^{2}$ of one of the photons, with $\ensuremath{-}{q}^{2}l7$ Ge${\mathrm{V}}^{2}$. This cross section falls much less rapidly with ${W}_{\ensuremath{\gamma}\ensuremath{\gamma}}$ than does the cross section for a similar process, $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}p\overline{p}$. No ${\ensuremath{\Delta}}^{0}{\overline{\ensuremath{\Delta}}}^{0}$ production is observed, and only a small fraction of the events at low ${W}_{\ensuremath{\gamma}\ensuremath{\gamma}}$ is consistent with $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\Delta}}^{++}{\overline{\ensuremath{\Delta}}}^{\ensuremath{-}\ensuremath{-}}$, ${\ensuremath{\Delta}}^{++}\overline{p}{\ensuremath{\pi}}^{\ensuremath{-}}$, or ${\overline{\ensuremath{\Delta}}}^{\ensuremath{-}\ensuremath{-}}p{\ensuremath{\pi}}^{+}$. In an expanded search through the same data, four events compatible with either $\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}(\ensuremath{\Lambda}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{\ensuremath{-}})$ or ${\ensuremath{\Sigma}}^{0}\overline{\ensuremath{\Lambda}}({\ensuremath{\Sigma}}^{0}\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma})$ production were found.