Exclusive Photoproduction $J/\psi$ in Peripheral Pb-Pb

TL;DR

This paper investigates the exclusive photoproduction of J/psi mesons in peripheral Pb-Pb collisions at LHC energies, testing the light-cone color dipole formalism across different scenarios and comparing results with ALICE data.

Contribution

It evaluates the robustness of the light-cone color dipole formalism in peripheral collisions using three different interaction scenarios and compares predictions with experimental measurements.

Findings

Scenario 3 shows the best agreement with ALICE data.

The formalism's accuracy varies with centrality class.

Peripheral collision modeling benefits from geometrical constraints.

Abstract

The exclusive photoproduction of the $J/\psi$ state is investigated in peripheral AA collisions for the energies available at the LHC, $\sqrt{s}=2.76$ TeV and $\sqrt{s}=5.02$ TeV. In order to evaluate the robustness of the light-cone color dipole formalism, previously tested in the ultraperipheral regime, the rapidity distribution and the nuclear modification factor ($R_{AA}$) were calculated for three centrality classes: 30%-50%, 50%-70% and 70%-90%. In the peripheral regime, three scenarios were considered. In the scenario 1, a similar formalism adopted in the UPC regime is used; in the scenario 2, one considers that only the spectators in the target are the ones that interact coherently with the photon; in the scenario 3, the photonuclear cross section is modified using the same geometrical constraints applyed in the scenario 2. The results obtained from the three scenarios were compared with the ALICE measurements (only $J/\psi$ at the moment), showing a better agreement in the more complete approach (scenario 3), mainly in the more central regions (30%-50% and 50%-70%) where the incertainty is smaller.