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Title: Measurement of R=σL/σT and the separated longitudinal and transverse structure functions in the nucleon-resonance region
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  1. 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 ( ψ ( 2 S ) ) and ground state ( J / ψ ) vector mesons is measured as a function of the charged-particle multiplicity in proton-lead ( p Pb ) 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 T < 30 GeV and in four rapidity ranges spanning 2.865 < y 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. 
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