Absorption mechanisms in photon induced two-body knockout

Abstract

Calculations have been performed for the $^{16}$O($γ$,pn) and the $^{16}$O($γ$,pp) reaction in the photon-energy range $E_γ$ = 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.