Single photo and electroproduction of pions at EBAC@JLAB

TL;DR

This paper presents a dynamical coupled-channels analysis of pion electroproduction data at energies up to 1.6 GeV, fitting the data by adjusting nucleon resonance amplitudes and examining meson cloud effects.

Contribution

It introduces a comprehensive coupled-channels model that accurately fits pion electroproduction data and analyzes meson cloud effects on nucleon resonance form factors.

Findings

Data fits achieved by adjusting helicity amplitudes for key N* states.

Meson cloud effects are significant and consistent with unitarity.

Model successfully describes reactions up to W=1.6 GeV.

Abstract

Within the Excited Baryon Analysis Center we have performed a dynamical coupled-channels analysis of the available $p(e,e' \pi)N$ data in the region of $W \leq $ 1.6 GeV and $Q^2 \leq$ 1.45 (GeV/c)$^2$. The channels included are $\gamma^* N$, $\pi N$, $\eta N$, and $\pi\pi N$ which has $\pi\Delta$, $\rho N$, and $\sigma N$ components. With the hadronic parameters of the model determined in our previous investigations of $\pi N\to \pi N$ reaction, we have found that the available data in the considered $W \leq $ 1.6 GeV region can be fitted well by only adjusting the bare $\gamma^* N \to N^*$ helicity amplitudes for the lowest $N^*$ states in $P_{33}$, $P_{11}$, $S_{11}$ and $D_{13}$ partial waves. The meson cloud effect, as required by the unitarity conditions, on the $\gamma^* N \to N^*$ form factors are examined.