Modeling the Impact Parameter Dependence of the nPDFs With EKS98 and EPS09 Global Fits

TL;DR

This paper introduces spatially dependent nuclear parton distribution functions (nPDFs) based on the A-dependence of EPS09 and EKS98 fits, enabling more precise modeling of nuclear effects in high-energy collisions.

Contribution

It develops new spatially dependent nPDF sets EPS09s and EKS98s, incorporating the nuclear geometry into the global fits for improved accuracy.

Findings

The new nPDF sets successfully describe centrality-dependent data at RHIC.

Predictions for LHC proton-lead collisions show significant nuclear modification effects.

Comparison with RHIC data validates the spatial dependence modeling.

Abstract

So far the nuclear PDFs (nPDFs) in the global DGLAP fits have been taken to be spatially independent. In this work, using the $A$-dependence of the globally fitted sets EPS09 and EKS98, we have determined the spatial dependence of the nPDFs in terms of powers of the nuclear thickness functions. New spatially dependent nPDF sets EPS09s (NLO, LO, error sets) and EKS98s (LO) are released. As an application, we consider the nuclear modification factor $R_{dAu}^{\pi^0}$ at midrapidity for neutral pion production in deuteron-gold collisions at RHIC in NLO. Comparison with the PHENIX data in different centrality classes is also shown. In addition, predictions for the corresponding nuclear modification factor $R_{pPb}^{\pi^0}$ in proton-lead collisions at the LHC are discussed.