Study of exclusive photoproduction of charmonium in ultra-peripheral lead-lead collisions

Abstract

The cross-sections of exclusive (coherent) photoproduction $J/\psi$ and $\psi (2S)$ mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of $5.02\mathrm{TeV}$ are measured using a data sample corresponding to an integrated luminosity of $228\pm 10{\mu \mathrm{b}}^{-1}$, collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for $J/\psi$ and $\psi (2S)$ mesons. The integrated cross-sections are measured to be \mbox{${\sigma }_{J/\psi }^{\mathrm{coh}}=5.965\pm 0.059\pm 0.232\pm 0.262\mathrm{mb}$} and \mbox{${\sigma }_{\psi (2S)}^{\mathrm{coh}}=0.923\pm 0.086\pm 0.028\pm 0.040\mathrm{mb}$}, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be \mbox{${\sigma }_{\psi (2S)}^{\mathrm{coh}}/{\sigma }_{J/\psi }^{\mathrm{coh}}=0.155\pm 0.014\pm 0.003$}, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-012.html (LHCb public pages)

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• Exclusive quarkonium photoproduction: predictions with the Balitsky-Kovchegov equation including the full impact-parameter dependence
• Probing gluon fluctuations in nuclei with the first energy-dependent measurement of incoherent J/$\psi$ photoproduction in ultraperipheral PbPb collisions
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