Pion photoproduction of nucleon excited states with Hamiltonian effective field theory

TL;DR

This paper refines calculations of pion photoproduction amplitudes using Hamiltonian effective field theory, incorporating coupled channels and resonance contributions, achieving results comparable to other models.

Contribution

It introduces an improved Hamiltonian effective field theory approach that includes coupled channels and resonance effects for pion photoproduction.

Findings

Enhanced multipole amplitude $E_{0+}$ results.

Computed $M_{1-}$ amplitude relevant to Roper resonance.

Results align with other dynamical coupled channel models.

Abstract

We refine our previous calculation of multipole amplitude $E_{0+}$ for pion photoproduction process, $\gamma N\rightarrow\pi N$. 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 $N^*(1650)$ and the $K\Lambda$ coupled channel. The contribution from the bare state corresponding to the $N^*(1650)$ 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.