Observation of the charged-particle multiplicity dependence of ${\sigma }_{\psi (2S)}/{\sigma }_{\text{J}/\psi }$ in pPb collisions at 8.16 TeV

Abstract

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 ($\psi$(2S)) and ground state (J/$\psi$) vector mesons is measured as a function of the charged-particle multiplicity in proton-lead (pPb) collisions at a center-of-mass (CM) energy per nucleon pair of 8.16 TeV. The data corresponding to an integrated luminosity of 175 nb${}^{-1}$ were collected using the CMS detector. The ratio is measured separately for prompt and nonprompt charmonia in the transverse momentum range 6.5 $<$ $p_{\text{T}}$ $<$ 30 GeV and in four rapidity ranges spanning $-$2.865 $<$ $y_{\text{CM}}$ $<$ 1.935. 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.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-24-001 (CMS Public Pages). This version corrects the CERN preprint number

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