Absorption mechanisms in photon induced two-body knockout

Calculations have been performed for the 16O(γ, pn) and the 16O(γ, pp) reaction in the photon-energy range Eγ =60–300 MeV. Besides the contribution from the more common photoabsorption on the pionic degrees of freedom, we have investigated the influence of heavier meson exchange (ϱ, σ, ω) and intermediate Δ creation with π and ϱ exchange. Whereas the π meson is found to set the main trends, the ϱ meson is found not to be discardable in a theoretical description of the (γ, pn) reaction. The incorporation of an energy dependence and a decay width in the Δ propagator is observed to be essential in order to arrive at a more realistic description of (γ, NN) reactions at higher photon energies.