Maqola

Exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> photoproduction in ultraperipheral Pb+Pb collisions at the CERN Large Hadron Collider calculated at next-to-leading order perturbative QCD

K. EskolaUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland and Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, FinlandChris A. FlettUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland and Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, FinlandV. GuzeyUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland and Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, FinlandTopi LöytäinenUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland and Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, FinlandHannu PaukkunenUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland and Helsinki Institute of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland

2022en

ABI

Annotatsiya

We present the first next-to-leading-order (NLO) perturbative QCD (pQCD) study of rapidity-differential cross sections of coherent exclusive photoproduction of $J/\ensuremath{\psi}$ mesons in heavy-ion ultraperipheral collisions (UPCs) at the CERN Large Hadron Collider (LHC), $d\ensuremath{\sigma}/dy(\text{Pb}+\text{Pb}\ensuremath{\rightarrow}\text{Pb}+J/\ensuremath{\psi}+\text{Pb})$. 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 $J/\ensuremath{\psi}$ photoproduction data in $\mathrm{Pb}+\mathrm{Pb}$ UPCs, exclusive $J/\ensuremath{\psi}$ photoproduction data from HERA, and LHCb data in $p+p$. The scale dependence in $d\ensuremath{\sigma}/dy(\text{Pb}+\text{Pb}\ensuremath{\rightarrow}\text{Pb}+J/\ensuremath{\psi}+\text{Pb})$ is significant, but we can find a scale choice that reproduces the $\mathrm{Pb}+\mathrm{Pb}$ UPC data at both 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.

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Identifikatorlar

DOI: 10.1103/physrevc.106.035202

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