Predictions for exclusive $\Upsilon$ photoproduction in ultraperipheral ${\rm Pb}+{\rm Pb}$ collisions at the LHC at next-to-leading order in perturbative QCD

TL;DR

This paper provides NLO QCD predictions for exclusive Upsilon photoproduction in ultraperipheral Pb+Pb collisions at the LHC, highlighting uncertainties from nPDFs and scale choices, and proposing a data-driven approach to improve accuracy.

Contribution

It introduces a NLO perturbative QCD framework for Upsilon photoproduction in heavy-ion collisions and proposes a data-driven method to reduce theoretical uncertainties.

Findings

NLO predictions show significant uncertainties from nPDFs and scale choices.

Data-driven approach reduces uncertainties and GPD modeling effects.

Process is predicted to be measurable at the LHC.

Abstract

We present predictions for the rapidity-differential cross sections of exclusive $\Upsilon$ photoproduction in ultraperipheral collisions (UPCs) of lead ions at the Large Hadron Collider (LHC). We work in the framework of collinear factorization at next-to-leading order (NLO) in perturbative QCD, modeling the generalized parton distributions (GPDs) through the Shuvaev transform of nuclear parton distribution functions (nPDFs). While the effects due to the GPD modeling turn out to be small, the direct NLO predictions still carry significant nPDF-originating uncertainties and depend strongly on the choices of the factorization and renormalization scales. To tame the scale dependence and to account for the fact that the NLO calculations generally underpredict the photoproduction measurements on protons, we also present alternative, data-driven predictions. In this approach the underlying photoproduction cross sections on lead are found by combining their nuclear modifications calculated at NLO with the measured photoproduction cross sections on protons. The data-driven strategy reduces the uncertainties associated with the scale choices, and essentially eliminates the effects of GPD modeling thereby leaving the cross sections sensitive mainly to the input nPDFs. Our estimates indicate that the process is measurable in ${\rm Pb}+{\rm Pb}$ collisions at the LHC.