Multiprocess imaging of nuclear modifications on parton distributions in proton-nucleus collisions

TL;DR

This paper introduces a novel imaging method for nuclear modifications of parton distribution functions in proton-nucleus collisions, using combined LHC observables to distinguish contributions from different parton types.

Contribution

It proposes a new approach to directly image nuclear modification factors at the observable level, enhancing the understanding of partonic structures in nuclei.

Findings

Validated method with NLO calculations and multiple nuclear PDF sets.

Demonstrated potential for future LHC measurements to constrain nuclear PDFs.

Enabled separation of light-quark, gluon, and heavy-flavor contributions.

Abstract

Nuclear modifications to collinear parton distribution functions are conventionally quantified by the ratios $ r^{\textrm{A}}_i(x,Q^2) = f^\textrm{A,proton}_i(x,Q^2) / f^\textrm{proton}_i(x,Q^2) $. For a given nucleus $A$, these ratios generally depend on the parton momentum fraction $ x $, the probing scale $ Q^{2} $, and the parton species $ i $. Determining these dependencies relies on a global analysis of diverse experimental data. However, in realistic observables, these dependencies are intricately intertwined, making their extraction challenging. In this paper, we propose a novel approach to effectively image the nuclear modification factors $ r^{\textrm{A}}_i(x,Q^2) $ at the observable level in proton-nucleus collisions at the Large Hadron Collider. Specifically, through a combined study of $ Z $-boson production, $ Z $+jet production, and $ Z+c $-jet production, we separately enhance signals arising from light-quark, gluon, and heavy-flavor (charm) distributions in nuclei. This enables us to effectively image the $ r^{\textrm{A}}_i(x,Q^2) $ for specific parton species. The feasibility of this method is validated through perturbative calculations at next-to-leading order in the strong coupling constant, employing three sets of nuclear PDF parametrizations: EPPS21, nCTEQ15, and TUJU19. Future measurements of these observables are expected to provide more efficient constraints on nuclear PDFs and yield new insights into the detailed partonic structures of nuclei.