Testing nuclear parton distributions with pA collisions at the LHC

TL;DR

This paper discusses how proton-nucleus collisions at the LHC can serve as a powerful tool to test the fundamental assumption of factorization in nuclear parton distribution functions, which is crucial for understanding QCD in nuclear environments.

Contribution

It proposes using LHC pA collision data to phenomenologically test the factorization assumption of nuclear PDFs, extending the validation beyond numerical fits.

Findings

LHC pA collisions can provide critical tests of nPDF factorization.

Current nPDFs rely on factorization assumptions that need experimental validation.

Proposed measurements could reveal non-linear QCD effects in nuclei.

Abstract

Global perturbative QCD analyses, based on large data sets from electron-proton and hadron collider experiments, provide tight constraints on the parton distribution function (PDF) in the proton. The extension of these analyses to nuclear parton distributions (nPDF) has attracted much interest in recent years. nPDFs are needed as benchmarks for the characterization of hot QCD matter in nucleus-nucleus collisions, and attract further interest since they may show novel signatures of non-linear density-dependent QCD evolution. However, it is not known from first principles whether the factorization of long-range phenomena into process-independent parton distribution, which underlies global PDF extractions for the proton, extends to nuclear effects. As a consequence, assessing the reliability of nPDFs for benchmark calculations goes beyond testing the numerical accuracy of their extraction and requires phenomenological tests of the factorization assumption. Here we argue that a proton-nucleus collision program at the LHC would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits.