Diffractive vector meson photo-production in oxygen--oxygen and neon--neon ultraperipheral collisions at energies available at the CERN Large Hadron Collider

TL;DR

This work applies the energy-dependent hotspot model within the dipole framework to diffractive vector-meson photoproduction in ultra-peripheral O–O and Ne–Ne collisions at $\sqrt{s_{NN}}=5.36$ TeV. By evaluating both coherent and incoherent channels for $\rho^{0}$ and $J/\psi$ across $W$, $|t|$, and rapidity, and using two nuclear density prescriptions per nucleus (O: Woods–Saxon and alpha-cluster; Ne: Woods–Saxon and PGCM bowling-pin), the study probes gluon saturation and nuclear geometry. A key finding is that the incoherent cross section exhibits nontrivial energy and $t$ dependencies that signal saturation onset, while the relative normalization and shape differences between nuclear models offer a powerful handle on the underlying nuclear structure. The results indicate that simultaneous measurements of $\rho^{0}$ and $J/\psi$ coherent and incoherent production in these light-ion UPCs can substantially constrain oxygen and neon density profiles and guide future electron–ion collider studies. The predicted UPC cross sections are directly testable with LHC data, providing an early test bed for saturation physics in light nuclei and for refining nuclear structure models.

Abstract

The energy-dependent hotspot model is used to predict cross sections for vector-meson diffractive photo-nuclear production off oxygen ($γ$O) and neon ($γ$Ne) that can be extracted from ultra-peripheral O--O and Ne--Ne collisions, recently recorded at the LHC. In both cases, two models are used to describe the nuclear shapes. Woods-Saxon prescriptions for O and Ne as well as an alpha-cluster description of O and a bowling-pin-like shape for Ne, according to the PGCM formalism. Predictions are presented for the dependence on the centre-of-mass energy of the photon--nucleus system, as well as on Mandelstam-$t$, of the cross sections for the coherent and the incoherent photo-nuclear production of $ρ^{0}$ and J/$ψ$ vector mesons. Furthermore, the rapidity dependence of the ultra-peripheral cross section is reported for all cases. It is found that the incoherent process provides a measurable signature for the approach to the gluon-saturation regime, and that the simultaneous determination of $ρ^{0}$ and J/$ψ$ coherent and incoherent production provides a strong constraint on nuclear models for both O and Ne.

Figures (9)

• Figure 1: A hotspot configuration for the cluster model of $^{16}$O (left) and the PGCM model of $^{20}$Ne (right) is shown. Both configurations were obtained at a Bjorken-$x$ of $10^{-5}$.
• Figure 2: Nuclear thickness functions, normalised to 1 at zero impact parameter, for the four models discussed in the text.
• Figure 3: Predictions of the energy-dependent hotspot model for the Mandelstam-$t$ dependence, at a fixed $W$, of coherent and incoherent $\gamma{\rm O}$ production of $\rho^{0}$ (left) and ${\rm J}/\psi$ (right) vector mesons for two nuclear models: Woods-Saxon and a tetrahedron of alpha nuclei.
• Figure 4: Predictions of the energy-dependent hotspot model for the energy dependence of coherent and incoherent $\gamma{\rm O}$ production of $\rho^{0}$ (left) and ${\rm J}/\psi$ (right) vector mesons for two nuclear models: Woods-Saxon and a tetrahedron of alpha nuclei.
• Figure 5: Predictions of the energy-dependent hotspot model for the energy dependence at fixed values of Mandelstam-$t$ of incoherent $\gamma{\rm O}$ production of $\rho^{0}$ (left) and ${\rm J}/\psi$ (right) vector mesons for two nuclear models: Woods-Saxon and a tetrahedron of alpha nuclei.