Exclusive production of proton-antiproton pairs in two-photon collisions

We report cross sections for the process γγ→pp¯ at center-of-mass energies W from 2.0 to 2.8 GeV. These results have been extracted from measurements of $e^{+}$ $e^{\mathrm{-}}$→$e^{+}$ $e^{\mathrm{-}}$pp¯ at an overall center-of-mass energy of 29 GeV, using the TPC/Two-Gamma facility at the SLAC storage ring PEP. Cross sections for the untagged mode [both photons nearly real] are shown to lie well above QCD predictions. Results are also presented for the single-tagged mode [one photon in the range 0.16$Q^2$${)}^2$].