$J/\mathrm{\Psi }$ photoproduction in peripheral $AA$ collisions

The exclusive photoproduction of the heavy vector mesons $J/\mathrm{\Psi }$ is investigated in the context of peripheral lead-lead collisions for the energies available at the LHC, $\sqrt{s}=2.76\mathrm{TeV}$ and $\sqrt{s}=5.02\mathrm{TeV}$. Using the light-cone color dipole formalism, the rapidity distribution was calculated in two centrality bins at 50%–70% and 70%–90% in order to evaluate its robustness in extrapolating down to a smaller impact parameter. A modified photon flux is introduced, without change in the photonuclear cross section in relation to the ultraperipheral (UPC) case. Results were obtained for the two regions analyzed, which presented a maximum difference of 27% in frontal rapidity for the two regions. Comparing the results for $\sqrt{s}=2.76\mathrm{TeV}$ and $\sqrt{s}=5.02\mathrm{TeV}$, an increase was verified of approximately half the one obtained in the ultraperipheral regime in the central rapidity region.

Figure 1

The b-dependence photon flux distribution for the different form factors of the lead nuclei.

Figure 2

Left: change of variables $b_1\to b_2$ and $\theta \to \alpha$. Right: sketch of the overlap region existing in the peripheral collisions.

Figure 3

Comparison between the usual photon flux (dashed line) and the effective photon flux (solid line) for the photon energy $\omega =10\mathrm{GeV}$.

Figure 4

Rapidity distribution for $J/\mathrm{\Psi }$ photoproduction at $\sqrt{s}=2.76\mathrm{TeV}$ using the GBW dipole model.

Figure 5

Rapidity distribution for $J/\mathrm{\Psi }$ photoproduction at $\sqrt{s}=5.02\mathrm{TeV}$ using the GBW dipole model.