A simple model for nuclear modification of parton distribution functions

TL;DR

The paper addresses nuclear modifications of parton distribution functions across the full Bjorken-$x$ range by integrating a $Q^2$-rescaling model with Fermi motion into a framework based on analytic LO proton PDFs derived from generalized DAS asymptotics. It performs a global fit to $F_2^A(x,Q^2)/F_2^D(x,Q^2)$ data to extract nucleus-dependent rescaling parameters for valence, nonsinglet, and singlet/gluon components, providing simple analytic expressions to obtain nuclear PDFs for any nucleus. The results reproduce DIS ratios across multiple targets, reveal shadowing and antishadowing behaviors that differ between quarks and gluons, and show reasonable alignment with some existing nuclear PDF predictions while diverging in the large-$x$ region. The approach offers a practical tool for predicting nPDFs in unmeasured nuclei and can be used for phenomenology in $pA$ and $AA$ collisions at current and future colliders, with guidance on where higher-precision data are needed to discriminate competing models.

Abstract

A model for nuclear medium modification of parton densities is presented. The approach is based on the global analysis of available deep inelastic scattering data for different nuclear targets within the rescaling model combined with taking into account the effects of Fermi motion. The scale dependence is implemented into the DGLAP-evolved quark and gluon densities in a proton derived analytically at the leading order of QCD coupling. By fitting the rescaling parameters to experimental data on the ratio $F_2^A(x,Q^2)/F_2^{A^\prime}(x,Q^2)$ for several nuclear targets $A$ and $A^\prime$, we obtain redictions for nuclear parton distributions, even for unmeasured nuclei. The effects of nuclear modifications are investigated with respect to the mass number $A$. Our results highlight distinct shadowing and antishadowing behaviors for gluons and quarks.

Figures (4)

• Figure 1: The rescaling parameters $\delta^A_\pm$ and $\delta^A_{NS}$ listed in Table \ref{['tbl:parameters1']} and fitted in accorgding to (\ref{['eq:fitA']}), (\ref{['eq:fitB']}) and (\ref{['eq:fitC']}) as a function of mass number $A$.
• Figure 2: The global fit results of structure function ratios $F_2^{A}(x, Q^2)/F_2^D(x, Q^2)$ between different nuclei targets $A$ and deutron. Experimental data are from EMCEMC-CCuSnEMC-CCa1EMC-CCa2EMC-Cu, NMCNMC-CCaovLiNMC-HeCCaCCaovLiNMC-LiCNMC-BeAlCaFeSnPbovCNMC-SnovC, SLACSLAC-Fe, BCDMSBCDMS-NFeBCDMS-Fe, E665E665-CCaPbE665-Xe, JLabJLab-HeCBe and CLASCLAS-CAlFePb.
• Figure 3: The global fit results of structure function ratios $F_2^{A}(x, Q^2)/F_2^{A^\prime}(x, Q^2)$ between different nuclei targets $A$ and $A^\prime$. Experimental data are from NMCNMC-HeCCaCCaovLiNMC-LiCNMC-CCaovLiNMC-BeAlCaFeSnPbovCNMC-SnovC.
• Figure 4: The predicted nuclear modification factors for parton distributions in several nuclear targets. The results for gluon nuclear modification predicted by the nIMP groupnIMP are shown for comparison.