Pion photo-production of nucleon excited states with Hamiltonian effective field theory

We refine our previous calculation of multipole amplitude E₀₊ for pion photo-production process, γ N→π N. The treatment of final state interactions is based upon an earlier analysis of pion-nucleon scattering within Hamiltonian effective field theory, supplemented by incorporating contributions from the N^*(1650) and the KΛ coupled channel. The contribution from the bare state corresponding to the N^*(1650) significantly enhances our results. Additionally, we also compute the multipole amplitude M₁₋, which is of direct relevance to the Roper resonance. The results are comparable with other dynamical coupled channel models, even though the contribution from the bare state (interpreted as a 2s excitation) in this channel is small because of its large mass.