Speaker
Description
We present new measurements from the ALICE experiment on exclusive processes in ultra-peripheral Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.36$ TeV. The coherent photoproduction of ${\rm J} / \psi$ and $\psi({\rm 2S})$ is measured differentially in rapidity to probe nuclear gluon distributions at low Bjorken-$x$ $\sim$ $10^{-2}$. A significant suppression relative to the impulse approximation is observed, providing a clear evidence of nuclear shadowing. Simultaneously, the exclusive dimuon production $\gamma\gamma\to\mu\mu$, a pure QED process, is measured. These results serve as a critical benchmark, demonstrating high sensitivity to the precise modeling of the intense electromagnetic photon flux, particularly for photon impact parameters near the nuclear radius. Together, these measurements provide insights into nuclear PDFs and advance the understanding of strong-field QED in heavy-ion collisions.
| Speaker confirmation | Yes |
|---|