Dynamical model of antishadowing of the nuclear gluon distribution

TL;DR

This paper develops a theoretical model for nuclear gluon antishadowing based on diffraction and parton merging, predicting a significant antishadowing effect in the gluon distribution within nuclei.

Contribution

It introduces a novel model linking shadowing and antishadowing through diffraction and parton merging, providing explicit predictions for gluon antishadowing in nuclei.

Findings

Antishadowing peaks at 15% for lead at x=0.05-0.1

Antishadowing effect spans a wide x-range from 10^{-4} to 0.2

Impact parameter dependence of antishadowing is slow

Abstract

We explore the theoretical observation that within the leading twist approximation, the nuclear effects of shadowing and antishadowing in non-perturbative nuclear parton distribution functions (nPDFs) at the input QCD evolution scale involve diffraction on nucleons of a nuclear target and originate from merging of two parton ladders belonging to two different nucleons, which are close in the rapidity space. It allows us to propose that for a given momentum fraction $x_P$ carried by the diffractive exchange, nuclear shadowing and antishadowing should compensate each other in the momentum sum rule for nPDFs locally on the interval $\ln (x/x_P) \le 1$. We realize this by constructing an explicit model of nuclear gluon antishadowing, which has a wide support in $x$, $10^{-4} < x < 0.2$, peaks at $x=0.05-0.1$ at the level of $\approx 15$\% for $^{208}$Pb at $Q_0^2=4$ GeV$^2$ and rather insignificantly depends on details of the model. We also studied the impact parameter $b$ dependence of antishadowing and found it to be slow.