Hard probes in heavy ion collisions at the LHC: PDFs, shadowing and $pA$ collisions

TL;DR

This paper reviews the role of proton-nucleus collisions at the LHC in understanding nuclear parton distributions, factorization, and novel QCD phenomena, emphasizing their importance for heavy ion physics.

Contribution

It provides a comprehensive overview of the experimental and theoretical issues related to PDFs, shadowing, and hard probes in $pA$ collisions at the LHC, highlighting new insights and challenges.

Findings

Assessment of factorization validity in nuclear collisions

Discussion of nuclear modifications to parton distributions

Identification of semi-hard probes with large nuclear effects

Abstract

This manuscript is the outcome of the subgroup ``PDFs, shadowing and $pA$ collisions'' from the CERN workshop ``Hard Probes in Heavy Ion Collisions at the LHC''. In addition to the experimental parameters for $pA$ collisions at the LHC, the issues discussed are factorization in nuclear collisions, nuclear parton distributions (nPDFs), hard probes as the benchmark tests of factorization in $pA$ collisions at the LHC, and semi-hard probes as observables with potentially large nuclear effects. Also, novel QCD phenomena in $pA$ collisions at the LHC are considered. The importance of the $pA$ program at the LHC is emphasized.