New probes of nuclear gluon dynamics through photoproduction of charm in inelastic ultra-peripheral Pb$\unicode{x2014}$Pb collisions with ALICE

Abstract

In an ultra-peripheral collision, a photon can interact with a gluon in the target nucleus and produce a pair of charm quarks, while the target nucleus breaks up (inelastic scattering). These charm quarks then fragment and are observed as open charm hadrons or vector mesons. This process has been used in e$\unicode{x2014}$p collisions to set stringent limits on the proton gluon distribution at low-$x$. The current measurements can provide similar constraints on the much less known nuclear gluon distributions. ALICE has measured the transverse momentum distribution of inelastically photoproduced ${\text{D}}^0$ at midrapidity, in Pb$\unicode{x2014}$Pb collisions at $\sqrt{s_{\text{NN}}}$=5.36 TeV. The distribution is measured down to $p_{\text{T}}$=0 for the first time. The results are compared to model calculations.

Proceedings of the XXXI International Conference on Ultra-relativistic Nucleus-Nucleus Collisions (Quark Matter 2025), Apr 6-12, 2025