Quark + Diquark Description of Nucleon Elastic Electromagnetic Form Factors

TL;DR

This paper develops a Poincaré-covariant quark-diquark model for nucleons that accurately reproduces electromagnetic form factors and predicts specific zeroes in form factor ratios, offering a refined approach to baryon structure analysis.

Contribution

It introduces a symmetry-preserving current within a quark-diquark framework that matches and improves upon existing three-body nucleon models for electromagnetic form factors.

Findings

Reproduces most three-body analysis results

Predicts a zero in G_E^p/G_M^p ratio

Predicts no zero in G_E^n/G_M^n ratio

Abstract

Working with a Poincar\'e-covariant quark + diquark, $q(qq)$, Faddeev equation approach to nucleon structure, a refined symmetry preserving current for electron + nucleon elastic scattering is developed. The parameters in the interaction current are chosen to ensure that the $q(qq)$ picture reproduces selected results from contemporary $3$-body analyses of nucleon elastic electromagnetic form factors. Although the subset of fitted results is small, the $q(qq)$ picture reproduces almost all the $3$-body predictions and often results in better agreement with available data. Notably, the $q(qq)$ framework predicts a zero in $G_E^p/G_M^p$, the absence of such a zero in $G_E^n/G_M^n$, and a zero in the proton's $d$-quark Dirac form factor. Derived $q(qq)$ results for proton flavour-separated light-front-transverse number and anomalous magnetisation densities are also discussed. With the $q(qq)$ framework thus newly benchmarked, one may proceed to comparisons with a broader array of $3$-body results. This may enable new steps to be made toward answering an important question, viz. is the quark + fully-interacting diquark picture of baryon structure only a useful phenomenology or does it come close to expressing robust features of baryon structure?