Dynamical diquarks in the ${\boldsymbol{\gamma^{(\ast)} p\to N(1535)\tfrac{1}{2}^-}}$ transition

TL;DR

This paper models the gamma* p to N(1535) transition using a covariant Faddeev equation with dynamical diquark correlations, revealing how diquark components influence electrocouplings and baryon structure insights.

Contribution

It introduces a symmetry-preserving contact interaction framework with dynamical diquark correlations to study the N(1535) transition, highlighting the sensitivity of electrocouplings to diquark composition.

Findings

Helicity amplitudes are sensitive to diquark component strengths.

Scalar, axial-vector, pseudoscalar, and vector diquarks significantly influence baryon structure.

The model provides insights into resonance electrocouplings and baryon internal dynamics.

Abstract

The $\gamma^{(\ast)}+p \to N(1535) \tfrac{1}{2}^-$ transition is studied using a symmetry-preserving regularisation of a vector$\,\otimes\,$vector contact interaction (SCI). The framework employs a Poincar\'e-covariant Faddeev equation to describe the initial and final state baryons as quark+di\-quark composites, wherein the diquark correlations are fully dynamical, interacting with the photon as allowed by their quantum numbers and continually engaging in breakup and recombination as required by the Faddeev kernel. The presence of such correlations owes largely to the mechanisms responsible for the emergence of hadron mass; and whereas the nucleon Faddeev amplitude is dominated by scalar and axial-vector diquark correlations, the amplitude of its parity partner, the $N(1535) \tfrac{1}{2}^-$, also contains sizeable pseudoscalar and vector diquark components. It is found that the $\gamma^{(\ast)}+p \to N(1535) \tfrac{1}{2}^-$ helicity amplitudes and related Dirac and Pauli form factors are keenly sensitive to the relative strengths of these diquark components in the baryon amplitudes, indicating that such resonance electrocouplings possess great sensitivity to baryon structural details. Whilst SCI analyses have their limitations, they also have the virtue of algebraic simplicity and a proven ability to reveal insights that can be used to inform more sophisticated studies in frameworks with closer ties to quantum chromodynamics.