Nucleon Resonance Electrocouplings from the CLAS Meson Electroproduction Data

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.