Photoproduction of π+ from 14N in the Δ(1232) region

The reaction 14N(γ,π+)14Cgs gas been calculated in the framework of an extended isobar doorway approach for photon energies Eγ = 200, 230, 260, 320 and 400 MeV. The ground states of 14N and 14C have been treated as open-shell nuclei with the realistic Huffman H1 wave function and the doorway space is spanned by vertical strokeΨ(A=13) x Δ > states. The nonresonant background contribution is calculated in the nonlocal DWIA in which the elementary pion production amplitude is obtained from the full Born terms with the M1+(3) part projected out and the distorted pion wave function is obtained in the extended doorway approach. Our results are considerably larger than standard DWIA calculations and give further improvement over more recent developments but are still lower than experimental data in the range between 230 and 320 MeV. Furthermore two-step processes with intermediate charge exchange as 14N(γ,π0)14Ngs(π0,π+)14Cgs have been calculated and found to be up to 13% in the maximum. (orig.)