Exclusive production of pp¯π+π- in photon-photon collisions

We report a measurement of the e⁺e^--->e⁺e^-pp¯π⁺π^- process with the TPC/Two-Gamma facility at the PEP e⁺e^- storage ring at SLAC. Forty-five pp¯π⁺π^- events were identified in data corresponding to an integrated e⁺e^- luminosity of 142 pb^-1. The cross section for γγ-->pp¯π⁺π^- is given both as a function of the γγ center-of-mass energy W_γγ, with W_γγ between 2.5 and 5.5 GeV, and as a function of the invariant mass squared q² of one of the photons, with -q²<7 GeV². This cross section falls much less rapidly with W_γγ than does the cross section for a similar process, γγ-->pp¯. No Δ⁰Δ¯ ⁰ production is observed, and only a small fraction of the events at low W_γγ is consistent with γγ-->Δ⁺⁺Δ¯ ^--, Δ⁺⁺p¯π^-, or Δ¯ ^--π⁺. In an expanded search through the same data, four events compatible with either ΛΛ¯ (Λ-->pπ^-) or Σ⁰Λ¯ (Σ⁰-->Λγ) production were found.