Structure of the Roper Resonance with Diquark Correlations

TL;DR

This paper models the electromagnetic properties of the nucleon and Roper resonance using a chiral quark-diquark framework, incorporating scalar and axial-vector diquarks to match experimental form factors and charge radii.

Contribution

It introduces a superposition-based quark-diquark model for nucleons and Roper resonance, including diquark intrinsic properties, to improve understanding of their electromagnetic form factors.

Findings

Proton and neutron electric form factors agree with experiments due to diquark sizes.

Magnetic moments are smaller than experimental values because of scalar dominance.

Charge radii of the Roper resonance are similar to those of the nucleon.

Abstract

We study electromagnetic properties of the nucleon and Roper resonance in a chiral quark-diquark model including two kinds of diquarks needed to describe the nucleon: scalar and axial-vector diquarks. The nucleon and Roper resonance are described as superpositions of two quark-diquark bound states of a quark and a scalar diquark and of a quark and an axial-vector diquark. Electromagnetic form factors of the nucleon and Roper resonance are obtained from one-loop diagrams where the quark and diquarks are coupled by a photon. We include the effects of intrinsic properties of the diquarks: the intrinsic form factors both of the diquarks and the anomalous magnetic moment of the axial-vector diquark. The electric form factors of the proton and neutron reasonably agree with the experiments due to the inclusions of the diquark sizes, while the magnetic moments become smaller than the experimental values because of the scalar dominance in the nucleon. The charge radii of the Roper resonance are almost comparable with those of the nucleon.