in pPb collisions with CMS and its implication regarding comover effects in small systems*

The substantial masses of charm hadrons make them exceptional tools for studying quantum chromodynamics (QCD), providing quantitative insights into QCD dynamics for systems with high parton densities and/or temperatures. Final-state effects, including interactions with co-moving particles or quark coalescence, may modify the hadronization of heavy quarks. To study these effects, we report the first measurement of prompt and non-prompt separated 𝜓(2S)/J/𝜓 cross-section ratios as a function of the charged-particle multiplicity in proton-lead (pPb) collisions at √s_NN = 8.16 TeV. For the first time in the pPb collision system, a multiplicity dependence of this ratio is observed for prompt charmonium production. The ratio of the nonprompt 𝜓(2S) to J/𝜓 cross sections show no dependency on multiplicity. The rapidity-dependence of this observable is studied, and results are compared with a model incorporating comover interactions. These measurements constrain hadronization models of heavy quarks in nuclear collisions and support a picture in which co-moving particles may dissociate the weakly-bound excited state of charmonia more than the ground state throughout the system’s evolution.