A compendium of cold-nuclear matter baseline predictions in light-ion collisions

Abstract

The recent light-ion collision programme at RHIC and the LHC provides a unique opportunity to investigate the onset of quark-gluon plasma formation and parton energy loss in small systems. A quantitative interpretation of emerging jet quenching measurements requires precise control over cold nuclear matter (CNM) effects, which modify hard-process cross sections independently of any hot-medium dynamics. In this work, we present a comprehensive set of perturbative QCD baseline calculations for nuclear modification factors (

) in proton-oxygen (pO), oxygen-oxygen (OO) and neon-neon (NeNe) collisions at LHC energies. The study includes charged hadron, neutral pion, prompt photon, and electroweak-boson production computed at next-to-leading order using a broad set of recent nuclear parton distribution functions (nPDFs). We demonstrate that CNM effects alone can induce sizeable suppressions in light-ion systems, with large associated nPDF uncertainties that currently limit the quantitative extraction of parton energy loss. To address this limitation, we explore a range of multi-cross-section ratios in which CNM effects and their uncertainties largely cancel. In particular, ratios of neutral pion

$$R_\textrm{OO}$$ R OO

to prompt photon

$$R_\textrm{OO}$$ R OO

or charged hadron

$$R_\textrm{OO}$$ R OO

to

$$R_\textrm{pO} ^2$$ R pO 2

provide theoretically robust observables with substantially reduced nPDF uncertainties, thereby enhancing sensitivity to possible energy-loss signatures.