Pion photoproduction of nucleon excited states with Hamiltonian effective field theory

Abstract

We refine our previous calculation of multipole amplitude $E_{0+}$ for pion photoproduction process, $\gamma N\to \pi N$. 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 $N^{\ast }(1650)$ and the $K\Lambda$ coupled channel. The contribution from the bare state corresponding to the $N^{\ast }(1650)$ significantly enhances our results. Additionally, we also compute the multipole amplitude $M_{1-}$, 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.

Comments: 14 pages, 9 figures, 3 tables