Dynamical coupled-channels analysis of 1H(e,e'pi)N reactions

TL;DR

This study performs a dynamical coupled-channels analysis of pion electroproduction data, revealing the significance of channel interactions and meson cloud effects on nucleon resonance form factors.

Contribution

It introduces a comprehensive coupled-channels model that fits experimental data by adjusting N* helicity amplitudes, highlighting the importance of meson cloud effects.

Findings

Good fit to data with minimal parameter adjustments.

Coupled-channels effects significantly influence cross sections.

Meson cloud effects impact N* form factors.

Abstract

We have performed a dynamical coupled-channels analysis of available p(e,e'pi)N data in the region of W < 1.6 GeV and Q^2 < 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 --> pi N, pi pi N reactions, we have found that the available data in the considered W < 1.6 GeV region can be fitted well by only adjusting the bare gamma^* N --> N^* helicity amplitudes for the lowest N^* states in P33, P11, S11 and D13 partial waves. The sensitivity of the resulting parameters to the amount of data included in the analysis is investigated. The importance of coupled-channels effect on the p(e,e' pi)N cross sections is demonstrated. The meson cloud effects, as required by the unitarity conditions, on the gamma^* N --> N^* form factors are also examined. Necessary future developments, both experimentally and theoretically, are discussed.