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| Format: | Preprint |
| Published: |
2025
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| Online Access: | https://arxiv.org/abs/2503.08903 |
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| _version_ | 1866918139573305344 |
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| author | CMS Collaboration |
| author_facet | CMS Collaboration |
| contents | Incoherent J/$ψ$ photoproduction in heavy ion ultraperipheral collisions (UPCs) provides a sensitive probe of localized, fluctuating gluonic structures within heavy nuclei. This study reports the first measurement of the photon-nucleon center-of-mass energy ($W_{γ\mathrm{N}}$) dependence of this process in PbPb UPCs at a nucleon-nucleon center-of-mass energy of 5.02 TeV, using 1.52 nb$^{-1}$ of data recorded by the CMS experiment. The measurement covers a wide $W_{γ\mathrm{N}}$ range of $\approx$ 40-400 GeV, probing gluons carrying a fraction $x$ of nucleon momentum down to an unexplored region of 6.5 $\times$ 10$^{-5}$. Compared to baseline predictions neglecting nuclear effects, the measured cross sections exhibit significantly greater suppression at lower $x$. Additionally, the ratio of incoherent to coherent photoproduction is found to be constant across the probed $W_{γ\mathrm{N}}$ and $x$ range, disfavoring the establishment of the black disk limit. This study provides critical insights into the $x$-dependent evolution of fluctuating gluonic structures within nuclei and calls for further advancements in theoretical models incorporating nuclear shadowing and gluon saturation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_08903 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Probing gluon fluctuations in nuclei with the first energy-dependent measurement of incoherent J/$ψ$ photoproduction in ultraperipheral PbPb collisions CMS Collaboration Nuclear Experiment High Energy Physics - Experiment Incoherent J/$ψ$ photoproduction in heavy ion ultraperipheral collisions (UPCs) provides a sensitive probe of localized, fluctuating gluonic structures within heavy nuclei. This study reports the first measurement of the photon-nucleon center-of-mass energy ($W_{γ\mathrm{N}}$) dependence of this process in PbPb UPCs at a nucleon-nucleon center-of-mass energy of 5.02 TeV, using 1.52 nb$^{-1}$ of data recorded by the CMS experiment. The measurement covers a wide $W_{γ\mathrm{N}}$ range of $\approx$ 40-400 GeV, probing gluons carrying a fraction $x$ of nucleon momentum down to an unexplored region of 6.5 $\times$ 10$^{-5}$. Compared to baseline predictions neglecting nuclear effects, the measured cross sections exhibit significantly greater suppression at lower $x$. Additionally, the ratio of incoherent to coherent photoproduction is found to be constant across the probed $W_{γ\mathrm{N}}$ and $x$ range, disfavoring the establishment of the black disk limit. This study provides critical insights into the $x$-dependent evolution of fluctuating gluonic structures within nuclei and calls for further advancements in theoretical models incorporating nuclear shadowing and gluon saturation. |
| title | Probing gluon fluctuations in nuclei with the first energy-dependent measurement of incoherent J/$ψ$ photoproduction in ultraperipheral PbPb collisions |
| topic | Nuclear Experiment High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2503.08903 |