Exclusive $J/\psi$ photoproduction in ultraperipheral Pb+Pb collisions at the LHC to next-to-leading order perturbative QCD

Abstract

We present the first next-to-leading-order (NLO) perturbative QCD (pQCD) study of rapidity-differential cross sections of coherent exclusive photoproduction of $J/\psi$ mesons in heavy-ion ultraperipheral collisions (UPCs) at the LHC, $d\sigma /dy(\text{Pb}+\text{Pb}\to \text{Pb}+J/\psi +\text{Pb})$. For this, we account for the photon-nucleon NLO cross sections at the forward limit, the $t$ dependence using a standard nuclear form factor, and the photon fluxes of the colliding nuclei. Approximating the generalized parton distributions with their forward-limit parton distribution functions (PDFs), we quantify the NLO contributions in the cross sections, show that the real part of the amplitude and quark-PDF contributions must not be neglected, quantify the uncertainties arising from the scale-choice and PDFs, and compare our results with ALICE, CMS and LHCb $J/\psi$ photoproduction data in Pb+Pb UPCs, exclusive $J/\psi$ photoproduction data from HERA, and LHCb data in p+p. The scale dependence in $d\sigma /dy(\text{Pb}+\text{Pb}\to \text{Pb}+J/\psi +\text{Pb})$ is significant, but we can find a scale-choice that reproduces the Pb+Pb UPC data both at 2.76 and 5.02 TeV collision energies. This process has traditionally been suggested to be a direct probe of nuclear gluon distributions. We show that the situation changes rather dramatically from LO to NLO: the NLO cross sections reflect the nuclear effects of both gluons and quarks in a complicated manner where the relative signs of the LO and NLO terms in the amplitude play a significant role.

22 pages, 13 figures

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• Probing small Bjorken-$x$ nuclear gluonic structure via coherent J/$\psi$ photoproduction in ultraperipheral PbPb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Energy dependence of coherent photonuclear production of J/$\psi$ mesons in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=5.02 TeV
• Overview of high-density QCD studies with the CMS experiment at the LHC
• Study of exclusive photoproduction of charmonium in ultra-peripheral lead-lead collisions
• Multi-scale Imaging of Nuclear Deformation at the Electron Ion Collider
• Next-to-leading order perturbative QCD predictions for exclusive $J/\psi$ photoproduction in oxygen-oxygen and lead-lead collisions at the LHC
• Observation of strong nuclear suppression in exclusive $J/\psi$ photoproduction in Au$+$Au ultra-peripheral collisions at RHIC
• Exclusive and dissociative J/$\psi$ photoproduction, and exclusive dimuon production, in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV
• Challenges to the Good-Walker paradigm in coherent and incoherent photoproduction
• Exclusive $J/\psi$, $\psi (2s)$, and $e^{+}{e}^{-}$ pair production in Au$+$Au ultra-peripheral collisions at RHIC
• Global Bayesian Analysis of $\mathrm{J}/\psi$ Photoproduction on Proton and Lead Targets
• Vector meson photoproduction in UPCs with FoCal
• Probing Quantum Phenomena through Photoproduction in Relativistic Heavy-Ion Collisions
• Measurement of coherent exclusive $J/\psi \to {\mu }^{+}{\mu }^{-}$ production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{\text{NN}}}=5.36$ TeV with the ATLAS detector