Speaker
Description
Ultraperipheral collisions (UPCs) of relativistic heavy ions provide a unique laboratory for studying photon-induced reactions due to their intense photon flux. Vector mesons, such as $J/\Psi$ and $\Psi(2S)$, can be produced via $\gamma$ + A interactions, offering a powerful tool for probing the gluonic properties of the target nucleus. The $J/\Psi$ and $\Psi(2S)$ mesons introduce distinct hard scales, providing unique capabilities for exploring QCD phenomena at different energy scales. In this talk, we present new results of coherent charmonium photoproduction spanning over a wide rapidity coverage in PbPb UPCs with $\sqrt{s_{\rm NN}} = 5.36$ TeV data taken with the CMS experiment during the LHC Run 3. This measurement represents a significant increase in statistics and improved $\Psi(2S)$ detection. The $\Psi(2S)$ are reconstructed from both the $J/\Psi$ + dipion channel, and the dilepton channel, and the $J/\Psi$ are reconstructed from the dilepton decay channel. These results include precise measurements of the coherent photoproduction cross sections for both $J/\Psi$ and $\Psi(2S)$ over the full 0 < |y| < 2.4 region, and exploit the forward neutron tagging technique to resolve the photon-emitter and target ambiguity. The expanded pseudorapidity coverage enables a more comprehensive exploration of the nuclear gluonic structure over a broad range of Bjorken-x values.
