Quark Structure of the Nucleon and Angular Asymmetry of Proton-Neutron Hard Elastic Scattering

TL;DR

This paper studies the angular asymmetry in proton-neutron elastic scattering to understand the nucleon's quark structure, finding that diquark models align with experimental data and offer insights into QCD-based nucleon models.

Contribution

It demonstrates that angular asymmetry measurements can distinguish between different quark wave function models of the nucleon, especially favoring the diquark picture over SU(6) symmetry.

Findings

Diquark model predicts asymmetry consistent with experimental data.

SU(6) symmetry model predicts opposite asymmetry to observations.

Angular asymmetry constrains the relative sign and magnitude of diquark components.

Abstract

We investigate an asymmetry in the angular distribution of hard elastic proton-neutron scattering with respect to 90deg center of mass scattering angle. We demonstrate that the magnitude of the angular asymmetry is related to the helicity-isospin symmetry of the quark wave function of the nucleon. Our estimate of the asymmetry within the quark-interchange model of hard scattering demonstrates that the quark wave function of a nucleon based on the exact SU(6) symmetry predicts an angular asymmetry opposite to that of experimental observations. On the other hand the quark wave function based on the diquark picture of the nucleon produces an asymmetry consistent with the data. Comparison with the data allowed us to extract the relative sign and the magnitude of the vector and scalar diquark components of the quark wave function of the nucleon. These two quantities are essential in constraining QCD models of a nucleon. Overall, our conclusion is that the angular asymmetry of a hard elastic scattering of baryons provides a new venue in probing quark-gluon structure of baryons and should be considered as an important observable in constraining the theoretical models.