Nucleon to Roper transition amplitudes and electromagnetic form factors

TL;DR

This paper investigates the properties and transition amplitudes of the Roper resonance, a nucleon excitation, using quark models and analyzes their behavior across different momentum transfer regions to better understand baryon structure.

Contribution

It provides a detailed analysis of the nucleon to Roper transition amplitudes and the role of baryon-meson states, offering insights into the Roper's nature within QCD frameworks.

Findings

Transition amplitudes are dominated by quark degrees of freedom at high Q^2.

Baryon-meson contributions are significant at low to intermediate Q^2.

The analytic structure of amplitudes helps explain experimental data.

Abstract

The second excitation of the nucleon, the Roper, has properties differentiated from other low-lying nucleon resonances. Their properties challenge our understanding of the structure of the baryons in terms of the degrees of freedom from QCD. In the present work we discuss the properties of the Roper resonance and the nucleon to Roper electromagnetic transition, based on the quark degrees of freedom, that are expected to dominate for large square momentum transfer $Q^2$. We also discuss the analytic structure of the transition amplitudes in the low-$Q^2$ region, and how the contributions of baryon-meson states can help to describe the low and intermediate $Q^2$ data, and the nature of the Roper.