Energy dependent nuclear suppression from gluon saturation in exclusive vector meson production

We calculate exclusive $\mathrm{J}/\psi$ photoproduction at high energies in the color glass condensate approach. The results are compared to the center-of-mass energy dependent $\gamma +A\to \mathrm{J}/\psi +A$ cross sections extracted from measurements in ultraperipheral heavy ion collisions at RHIC and LHC. We predict strong saturation-driven nuclear suppression at high energies, while LHC data prefer even stronger suppression. We explore effects of nucleon shaped fluctuations and show that the most recent measurement of the $|t|$-differential incoherent $\mathrm{J}/\psi$ cross section prefers large event-by-event fluctuations of the nucleon substructure in heavy nuclei, comparable to that found for a free proton.

Figure 1

Coherent $\mathrm{J}/\psi$ photoproduction cross section in ultraperipheral $\mathrm{Pb}+\mathrm{Pb}$ collisions compared to the ALICE [13], CMS [14], and LHCb [15] data. The bands represent the statistical uncertainty of the calculation.

Figure 2

Center-of-mass energy dependence of the coherent $\mathrm{J}/\psi$ photoproduction cross section compared to the ALICE [16], CMS [14], and scaled STAR [17, 18] data.

Figure 3

Suppression factor for coherent production compared to the ALICE [16] and CMS data [14].

Figure 4

Energy dependence of $S_{\text{incoh}}$ as defined in (7) for Pb nuclei calculated from the CGC setup and compared to STAR data [17, 18] for Au targets. The proton reference is always calculated with substructure fluctuations.

Figure 5

Incoherent $\mathrm{J}/\psi$ production in $\gamma +\mathrm{Pb}$ collisions at midrapidity compared to the ALICE data [56].