Impact of CMS dijets in 5.02 TeV pPb and pp collisions on EPPS16 nuclear PDFs

TL;DR

This paper analyzes CMS dijet data at 5.02 TeV to improve understanding of nuclear gluon PDFs, showing the data's consistency with EPPS16 modifications and revealing new insights into gluon behavior at various x values.

Contribution

It introduces a non-quadratic Hessian reweighting method to assess the impact of CMS dijet data on nuclear PDFs, refining the EPPS16 gluon modifications.

Findings

Stronger evidence for mid-x gluon antishadowing.

Indications of larger gluon shadowing at small x.

Enhanced constraints on gluon PDFs in the EMC region.

Abstract

The CMS measurement of dijet pseudorapidity distributions in pPb versus pp collisions at 5.02 TeV provides a direct probe on nuclear gluon PDFs. We show that while the predicted pPb pseudorapidity distributions suffer from sizable free-proton PDF uncertainties, the ratios of the pPb and pp distributions are practically insensitive to scale and free-proton PDF choices. We find the CMS data on pPb to pp ratios to be in good agreement with the EPPS16 nuclear modifications. Using a non-quadratic extension of the Hessian PDF reweighting method, we study the impact of these data on the EPPS16 nuclear PDFs. Relative to EPPS16, we find stronger evidence for mid-x gluon antishadowing as well as indication for larger gluon shadowing at small x. The data are also able to further constrain the gluon PDF in the EMC region.