Exclusive proton-antiproton production in two-photon collisions

Production of proton-antiproton pairs by two-photon scattering has been observed at the electron-position storage ring PETRA. A total of eight proton-antiproton pairs have been identified using the time-of-flight technique. We have measured a total cross section of 4.5 ± 0.8 nb in the photon-photon c.m. energy range 2.0-2.6 GeV. © 1982

Angular correlations in γγ→ρ⁰ρ⁰ near threshold

We present an analysis of ρ0ρ0 production by two photons in the ρ0ρ0 invariant mass range from 1.2 to 2.0 GeV. From a study of the angular correlations in the process γγ→ρ0ρ0→π- π+π- we exclude a dominant contribution from JP=0- or 2- states. The data indicate sizeable contributions from JP=0+ for four pion masses M4π1.7 GeV. The data are also well described by a model with isotropic production and uncorrelated isotropic decay of the ρ0,s. The cross section stays high below the nominal ρ0ρ0 threshold, i.e. M4π<1.5 GeV. The matrix element for ρ0ρ0 production is found to decrease steeply with increasing M4π. Upper limits for the couplings of the ι(1440) and Θ(1640) to γγ and ρ0ρ0 are given:Γ(ι→γγ)·B(ι→ρ 0ρ0)<1.0 keV and Γ(Θ→γγ) © 1982 Springer-Verlag