N* Experiments and their Impact on Strong QCD Physics

TL;DR

This paper reviews experimental studies of nucleon excited states using electromagnetic probes, highlighting their internal structure, transition form factors, and implications for understanding strong QCD dynamics and three-quark core nature.

Contribution

It provides a comprehensive overview of recent experimental results on nucleon excitations and their connection to theoretical models of strong QCD, emphasizing the role of electromagnetic interactions.

Findings

Experimental data supports the three-quark core model of nucleon resonances.

Transition form factors vary with photon virtuality, revealing internal structure.

Results connect experimental observations with sQCD modeling approaches.

Abstract

I give a brief overview of experimental studies of the spectrum and the structure of the excited states of the nucleon and what we learn about their internal structure. The focus is on the effort to obtain a more complete picture of the light-quark baryon excitation spectrum employing electromagnetic beams, and on the study of the transition form factors and helicity amplitudes and their dependence on the magnitude of the photon virtuality $Q^2$, especially for some of the most prominent resonances. The results were obtained in pion and eta electroproduction experiments off proton targets. They strengthen the connection of experiment and new results from modeling sQCD in DSE and Light Cone SR approaches. They also point to the nature of these states as 3-quark excitations at the core.