Coherent photoproduction of $J/\psi$ in nucleus-nucleus collisions in the color dipole approach

We investigate the exclusive photoproduction of $J/\psi$ mesons in ultraperipheral heavy-ion collisions in the color dipole approach. We first test a number of dipole cross sections fitted to inclusive $F_2$ data against the total cross section of exclusive $J/\psi$ production on the free nucleon. We then use the color dipole formulation of Glauber-Gribov theory to calculate the diffractive amplitude on the nuclear target. The real part of the free-nucleon amplitude is taken into account consistent with the rules of Glauber theory. We compare our results to recent published and preliminary data on exclusive $J/\psi$ production in ultraperipheral lead-lead collisions at $\sqrt{s_{NN}}=2.76$ and $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Especially at high-$\gamma A$ energies there is room for additional shadowing corrections, corresponding to triple-Pomeron terms or shadowing from large mass diffraction.

Figure 1

Coherent photoproduction of a vector meson in which the nucleus stays in its ground state.

Figure 2

Total cross section for the exclusive photoproduction $\gamma p\to J/\psi p$ as a function of $\gamma p-\mathrm{c}.\mathrm{m}.\mathrm{system}$ energy $W$. The data are from Refs. [41, 42, 43, 44, 45, 46, 47, 48, 49]. The results for three different dipole cross sections are shown.

Figure 3

Exclusive photoproduction in ultraperipheral heavy-ion collisions.

Figure 4

Rapidity-dependent cross-section $d\sigma /dy$ for exclusive production of $J/\psi$ in ${}^{208}\mathrm{Pb}{}^{208}\mathrm{Pb}$ collisions at per-nucleon c.m. system energy $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. The data are from the ALICE [2, 3] and CMS [4] Collaborations.

Figure 5

Rapidity-dependent cross-section $d\sigma /dy$ for exclusive production of $J/\psi$ in ${}^{208}\mathrm{Pb}{}^{208}\mathrm{Pb}$ collisions at per-nucleon c.m. system energy $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Shown are preliminary data are from the ALICE Collaboration [5].

Figure 6

Rapidity-dependent cross-section $d\sigma /dy$ for exclusive production of $J/\psi$ in ${}^{208}\mathrm{Pb}{}^{208}\mathrm{Pb}$ collisions at per-nucleon c.m. system energy $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Shown are preliminary data are from the LHCb Collaboration [6].

Figure 7

The total cross-section $\sigma (\gamma A\to J/\psi A)$ for the ${}^{208}\mathrm{Pb}$ nucleus as a function of $\gamma A-\mathrm{c}.\mathrm{m}.$ energy $W$. The data are from Ref. [54].