Nuclear PDF constraints from p+Pb collisions at the LHC

TL;DR

This paper discusses how p+Pb collision data from the LHC can enhance nuclear parton distribution function (PDF) constraints, especially for small-x gluons, by analyzing various measurements like inclusive hadron production and dijet data.

Contribution

It introduces the potential of LHC p+Pb collision data to improve nuclear PDF fits, focusing on small-x gluon uncertainties and proposing specific measurements for better constraints.

Findings

LHC p+Pb data can significantly improve small-x gluon nuclear PDFs.

Inclusive hadron and dijet measurements are sensitive to gluon modifications.

CMS dijet data can reduce uncertainties in nuclear gluon distributions.

Abstract

As the current nuclear PDF analyses are mainly constrained by fixed-target Drell-Yan and deeply inelastic scattering data only the quark nuclear modifications at fairly large $x$ values are in a good control. Inclusive pion production in d+Au collisions at RHIC provides some constraints for gluons but due to the limited kinematic reach of the data the gluon modifications remain uncertain especially at small values of $x$. In this talk, we discuss how the existing data from p+Pb collisions at the LHC can improve the nuclear PDF fits and which measurements would be sensitive to the small-$x$ gluons. In particular, we consider inclusive hadron production, compare this to direct photons, and show estimates of the effect of CMS dijet measurements to the uncertainty of nuclear gluon distributions.