# Extraction of Electromagnetic Transition Form Factors for Nucleon Resonances within a Dynamical Coupled-Channels Model - Nuclear Theory

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Abstract: We explain the application of a recently developed analytic continuationmethod to extract the electromagnetic transition form factors for the nucleonresonances $N^*$ within a dynamical coupled-channel model of meson-baryonreactions.Illustrative results of the obtained $N^* ightarrow \gamma N$transition form factors, defined at the resonance pole positions on the complexenergy plane, for the well isolated $P {33}$ and $D {13}$, and the complicated$P {11}$ resonances are presented. A formula has been developed to give anunified representation of the effects due to the first two $P {11}$ poles,which are near the $\pi\Delta$ threshold, but are on different Riemann sheets.We also find that a simple formula, with its parameters determined in theLaurent expansions of $\pi N ightarrow \pi N$ and $\gamma N ightarrow\pi N$amplitudes, can reproduce to a very large extent the exact solutions of theconsidered model at energies near the real parts of the extracted resonancepositions. We indicate the differences between our results and those extractedfrom the approaches using the Breit-Wigner parametrization of resonantamplitudes to fit the data.

Autor: N. Suzuki, T. Sato, T.-S. H. Lee

Fuente: https://arxiv.org/