Nucleon Resonance Electrocouplings from the CLAS Meson Electroproduction Data

TL;DR

This paper reports on the extraction of nucleon resonance electrocouplings from CLAS meson electroproduction data, providing new insights into the structure of excited proton states below 1.8 GeV and above 1.6 GeV.

Contribution

It presents the first determination of electrocouplings for high-mass $N^*$ states from CLAS data and compares results with theoretical models, highlighting the quark core and meson-baryon cloud contributions.

Findings

Consistent electrocouplings obtained from multiple channels.

First electrocouplings for $N^*$ states above 1.6 GeV.

Evidence supporting a quark core plus meson-baryon cloud structure.

Abstract

Transition helicity amplitudes $\gamma_{v}NN^*$ (electrocouplings) were determined for prominent excited proton states with masses below 1.8 GeV in independent analyses of major meson electroproduction channels: $\pi^{+}n$, $\pi^0p$ and $\pi^+\pi^-p$. Consistent results on resonance electrocouplings obtained from analyses of these exclusive reactions with different non-resonant contributions demonstrate reliable extraction of these fundamental quantities for states that have significant decays for either $N\pi$ or $N\pi\pi$ channels. Preliminary results on electrocouplings of $N^*$ states with masses above 1.6 GeV have become available from the CLAS data on $\pi^+\pi^-p$ electroproduction off protons for the first time. Comparison with quark models and coupled-channel approaches strongly suggest that $N^*$ structure is determined by contributions from an internal core of three constituent quarks and an external meson-baryon cloud at the distances covered in these measurements with the CLAS detector.