Proton quark distributions from a light-front Faddeev-Bethe-Salpeter approach

TL;DR

This paper uses a light-front Faddeev-Bethe-Salpeter approach with constituent quarks to model proton structure, reproducing form factors and parton distributions, and highlighting the importance of higher Fock states.

Contribution

It introduces a light-front Faddeev-Bethe-Salpeter model with a contact diquark interaction to study proton quark distributions, emphasizing the role of higher Fock components.

Findings

The model reproduces proton form factors and mass.

Spin degrees of freedom are not crucial for valence distributions.

Higher Fock states are needed for accurate parton distribution fits.

Abstract

The projection onto the Light-Front of a Minkowski space Faddeev-Bethe-Salpeter equation model truncated at the valence level is applied to study the proton structure with constituent quarks. The dynamics of the model has built-in: (i) a bound diquark brought by a contact interaction, and (ii) the separation by \Lambda_QCD of the infrared and ultraviolet interaction regions. The model parameters are fine tuned to reproduce the proton Dirac electromagnetic form factor and mass. From that, the non-polarized longitudinal and transverse momentum distributions were computed. The results for the evolved non-polarized valence parton distributions suggest that: (i) the explicit consideration of the spin degree of freedom of both quark and diquark seems not relevant to it, and (ii) the comparison with the global fit from the NNPDF4.0 calls for higher Fock components of the wave function beyond the valence one.