Proton-Nucleus Collisions at the LHC: Scientific Opportunities and Requirements

TL;DR

The paper argues that proton-nucleus collisions are crucial both as baseline measurements for the heavy-ion program and as a gateway to studying the proton and nuclear partonic structure at small x. It synthesizes accelerator requirements for asymmetric p+A collisions, current nuclear PDF uncertainties, and benchmark cross sections, and highlights opportunities in parton saturation and ultra-peripheral collisions with implications for astrophysics. By outlining the experimental and planning considerations for a LHC p+A run, it aims to guide strategic decisions to maximize scientific return in the high-energy nuclear physics program. Overall, the work reinforces the dual role of p+A data in clarifying PbPb interpretations and enriching QCD studies at the LHC.

Abstract

Proton-nucleus (p+A) collisions have long been recognized as a crucial component of the physics programme with nuclear beams at high energies, in particular for their reference role to interpret and understand nucleus-nucleus data as well as for their potential to elucidate the partonic structure of matter at low parton fractional momenta (small-x). Here, we summarize the main motivations that make a proton-nucleus run a decisive ingredient for a successful heavy-ion programme at the Large Hadron Collider (LHC) and we present unique scientific opportunities arising from these collisions. We also review the status of ongoing discussions about operation plans for the p+A mode at the LHC.