Pion photoproduction of nucleon excited states with Hamiltonian effective field theory

We refine our previous calculation of multipole amplitude 𝐸0+ for pion photoproduction 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 𝐾⁢Λ 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 2⁢𝑠 excitation) in this channel is small because of its large mass.