Investigating subnucleonic structures via new measurements of incoherent J/$\psi$ photoproduction in ultra-peripheral Pb--Pb collisions with ALICE

Abstract

Ultra-peripheral collisions of heavy ions provide a unique environment to study the gluon structure of nuclei through photon-induced reactions. In particular, the incoherent photoproduction of J/$\psi$ vector meson is sensitive to event-by-event fluctuations of the gluon field at nucleon and subnucleonic scales. We report new ALICE measurement of incoherent J/$\psi$ production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, differential in both photon-nucleus energy and Mandelstam-$|t|$. At low $|t|$, the cross section rises with increasing photon-nucleus energy, while at larger $|t|$ the growth is suppressed with respect to the trend at low $|t|$. This measurement represents the first study of incoherent photoproduction at the LHC performed as a function of both $W_{\gamma \mathrm{Pb},n}$ and $|t|$.

4 pages, 2 figures. Proceedings of the Quark Matter 2025 conference (QM2025)