Nucleon Resonance Structure Studies Via Exclusive KY Electroproduction

TL;DR

This paper discusses the importance of studying nucleon excited states through exclusive electroproduction channels, emphasizing the role of $KY$ channels and CLAS12 measurements in understanding the non-perturbative strong interaction.

Contribution

It introduces a program using CLAS12 to measure differential cross sections and polarization observables for $N^*$ states, expanding analysis into the previously unexplored high $Q^2$ domain.

Findings

Electrocouplings of $N^*$ states below 1.8 GeV have been determined from multiple channels.

$KY$ channels provide an independent means to analyze high-lying $N^*$ states.

CLAS12 will measure cross sections up to $Q^2$ of 12 GeV$^2$ for $N^*$ states.

Abstract

Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^*$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $\pi N$, $\eta N$, and $\pi \pi N$ data. This work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^*$ electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^*$ states preferentially decay through the $\pi \pi N$ channel instead of $\pi N$. Data from the $KY$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^*$ states against those determined from the $\pi N$ and $\pi \pi N$ channels. A program to study excited $N^*$ state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the $\gamma_vNN^*$ electrocoupling amplitudes for the most prominent $N^*$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^2$ up to 12~GeV$^2$.