A perturbative QCD study of dijets in p+Pb collisions at the LHC

TL;DR

This paper investigates dijet production in p+Pb collisions at the LHC using perturbative QCD, focusing on the sensitivity of certain observables to nuclear gluon modifications and their potential to constrain nuclear PDFs.

Contribution

It provides a detailed perturbative QCD analysis of dijet observables in p+Pb collisions, highlighting their sensitivity to nuclear gluon distributions and their use in testing collinear factorization.

Findings

Dijet rapidity distribution shape is stable within 5% uncertainty.

The ratio of yields in positive and negative rapidity is highly stable.

Observables are sensitive to nuclear modifications of gluon PDFs.

Abstract

Inspired by the recent measurements of the CMS collaboration, we report a QCD study of dijet production in proton+lead collisions at the LHC involving large-transverse-momentum jets, $p_T \gtrsim 100$ GeV. Examining the inherent uncertainties of the next-to-leading order perturbative QCD calculations and their sensitivity to the free proton parton distributions (PDFs), we observe a rather small, typically much less than 5% clearance for the shape of the dijet rapidity distribution within approximately 1.5 units around the midrapidity. Even a more stable observable is the ratio between the yields in the positive and negative dijet rapidity, for which the baseline uncertainty can be made negligible by imposing a symmetric jet rapidity acceptance. Both observables prove sensitive to the nuclear modifications of the gluon distributions, the corresponding uncertainties clearly exceeding the estimated baseline uncertainties from the free-proton PDFs and scale dependence. From a theoretical point of view, these observables are therefore very suitable for testing the validity of the collinear factorization and have a high potential to provide precision constraints for the nuclear PDFs.