Probing Small Bjorken-$\mathcal{x}$ Nuclear Gluonic Structure via Coherent $J/ψ$ Photoproduction in Ultraperipheral Pb-Pb Collisions at $\sqrt{s_{NN}} = 5.02$ $\mathrm{TeV}
Quasireal photons exchanged in relativistic heavy ion interactions are powerful probes of the gluonic structure of nuclei. The coherent J/ψ photoproduction cross section in ultraperipheral lead-lead collisions is measured as a function of photon-nucleus center-of-mass energies per nucleon (W$^{Pb}_{...
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Veröffentlicht in: | Physical review letters 2023-12, Vol.131 (26) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | Quasireal photons exchanged in relativistic heavy ion interactions are powerful probes of the gluonic structure of nuclei. The coherent J/ψ photoproduction cross section in ultraperipheral lead-lead collisions is measured as a function of photon-nucleus center-of-mass energies per nucleon (W$^{Pb}_{\gamma N}$) over a wide range of 40 < W$^{Pb}_{\gamma N}$ < 400 GeV. Results are obtained using data at the nucleon-nucleon center-of-mass energy of 5.02 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 1.52 nb -1. The cross section is observed to rise rapidly at low W$^{Pb}_{\gamma N}$, and plateau above W$^{Pb}_{\gamma N}$ ≈ 40 GeV, up to 400 GeV, entering a new regime of small Bjorken-$\mathcal{x}$ ( ≈ 6 x 10-5) gluons being probed in a heavy nucleus. The observed energy dependence is not predicted by current quantum chromodynamic models. |
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ISSN: | 0031-9007 |