Testing factorization in pA collisions at the LHC

TL;DR

This paper proposes that a proton-nucleus collision program at the LHC, including a rapidity scan, can provide critical tests of the factorization assumption in nuclear parton distribution functions, which is essential for reliable QCD predictions.

Contribution

It introduces a phenomenological approach to test the factorization assumption in nuclear PDFs using LHC proton-nucleus collision data, including rapidity scans.

Findings

Proposes using LHC pA collision data to test factorization in nPDFs.

Highlights the importance of rapidity scans for these tests.

Suggests this approach can validate the reliability of nPDFs in QCD calculations.

Abstract

Global perturbative QCD analyses, based on large data sets from e-p 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 programme at the LHC, including a rapidity scan, would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits.