Observation of the Charged-Particle Multiplicity Dependence of (Formula presented) in (Formula presented)-Pb Collisions at 8.16 TeV

Bound states of charm and anticharm quarks, known as charmonia, have a rich spectroscopic structure that can be used to probe the dynamics of hadron production in high-energy hadron collisions. Here, the cross section ratio of excited (Formula presented) and ground state (Formula presented) vector mesons is measured as a function of the charged-particle multiplicity in proton-lead ((Formula presented)) collisions at a center-of-mass (CM) energy per nucleon pair of 8.16 TeV. The data corresponding to an integrated luminosity of (Formula presented) were collected using the CMS detector. The ratio is measured separately for prompt and nonprompt charmonia in the transverse momentum range (Formula presented) and in four rapidity ranges spanning (Formula presented). For the first time, a statistically significant multiplicity dependence of the prompt cross section ratio is observed in proton-nucleus collisions. There is no clear rapidity dependence in the ratio. The prompt measurements are compared with a theoretical model which includes interactions with nearby particles during the evolution of the system. These results provide additional constraints on hadronization models of heavy quarks in nuclear collisions.