Medium modifications of the bound nucleon GPDs and the quark contribution to the spin sum rule

TL;DR

This paper investigates how the nuclear medium alters the quark contributions to the nucleon spin sum rule using generalized parton distributions derived from a quark-meson coupling model, revealing significant density-dependent modifications.

Contribution

It introduces a model for bound nucleon GPDs based on elastic form factors, providing insights into medium effects on nucleon spin structure relevant for incoherent DVCS experiments.

Findings

J^{q*} increases by 7% at nuclear saturation density

L^{q*} increases by 20% at nuclear saturation density

ΔΣ* decreases by 17% at nuclear saturation density

Abstract

We estimate the nuclear medium modifications of the quark contribution to the bound nucleon spin sum rule, J^{q*}, as well as the separate helicity, \Delta \Sigma*, and the angular momentum, L^{q*}, contributions to J^{q*}. For the calculation of the bound nucleon generalized parton distributions (GPDs), we use as input the bound nucleon elastic form factors predicted in the quark-meson coupling model. Our model for the bound nucleon GPDs is relevant for incoherent deeply virtual Compton scattering (DVCS) with nuclear targets. We find that the m5Aedium modifications increase J^{q*} and L^{q*} and decrease \Delta \Sigma* compared to the free nucleon case. The effect is large and increases with increasing nuclear density \rho. For instance, at \rho=\rho_0=0.15 fm^{-3}, J^{q*} increases by 7%, L^{q*} increases by 20%, and \Delta \Sigma* decreases by 17%. These in-medium modifications of the bound nucleon spin properties may be understood qualitatively in terms of the enhancement of the lower component of the quark Dirac spinor in the nuclear medium.