Influence of the Δ-isobar excitation on ( γ, p) reactions at medium energy

The major purpose of the present paper is to study medium energy ( γ,p) reaction mechanisms. Differential cross-section calculations are performed in a picture which includes both direct reaction process and an excitation of Δ-isobar-hole states. It is shown that simple PWIA calculation cannot give a good fit to the data, but the Δ-h result is in reasonable agreement with experiment. This means that the role of Δ intermediate excitation in the ( γ,p) reaction is significant. Some discussions about obtained results are also given in the paper