Collision geometry in UPC dijet production

TL;DR

This paper provides a detailed NLO pQCD analysis of inclusive dijet photoproduction in ultraperipheral heavy-ion collisions, emphasizing the importance of collision geometry and photon flux modeling for accurate cross section predictions.

Contribution

It introduces a comprehensive NLO pQCD framework that incorporates finite nuclear size effects, impact parameter dependence, and electromagnetic breakup survival factors for UPC dijet production.

Findings

Dijet production at large z_gamma is sensitive to small impact parameters.

Cross section predictions depend on collision geometry and photon flux modeling.

Impact-parameter dependent nuclear PDFs can be probed with this process.

Abstract

We present a comprehensive NLO pQCD study on inclusive dijet photoproduction in ultraperipheral nucleus-nucleus collisions (UPCs). Our analysis takes into account the finite size of both the photon-emitting and the target nucleus, estimated using the Wood-Saxon nuclear density profile. We show that a significant part of the measured dijets at large $z_\gamma$ in UPC Pb+Pb collisions at 5.02 TeV come from events with relatively small impact parameters of the order of a few nuclear radii, and the cross section predictions thus become sensitive to the modelling of the collision geometry and photon flux near the source nucleus. In addition, we include the modelling of electromagnetic breakup survival factor needed for a direct comparison with the experimental data and study the resolution power of this process in terms of the impact-parameter dependent nuclear parton distribution functions.