Erlangen 2026 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 23: Heavy-Ion Collisions and QCD Phases III
HK 23.5: Vortrag
Mittwoch, 18. März 2026, 15:00–15:15, PHIL C 301
Charmonium production as a function of multiplicity in pp collisions — •Alexander Tiekötter for the ALICE Germany collaboration — Institut für Kernphysik, Münster, Deutschland
Charmonium production happens at different energy scales. cc production occurs at perturbative energies, while the hadronization into colorless charmonium is a soft process. Models like the Improved Color Evaporation Model or Non-relativistic QCD describe the charmonium cross-section well, but fail at pT < 3 GeV/c. The color glass condensate (CGC) approach extends NRQCD to better describe the low pT regime and implies a non-linear multiplicity dependence of charmonium production.
To investigate this effect, we measure the production of J/ψ and ψ(2S) mesons at √s = 13.6 TeV as a function of charged-particle multiplicity with the ALICE detector at mid-rapidity in the e+e− decay channel. The multiplicity is measured by using an iterative Bayesian unfolding algorithm to convert the number of tracks to a charged-particle distribution. Results are presented via self-normalized ratios so that experiment-dependent quantities cancel. Results of the inclusive J/ψ production as function of multiplicity show a stronger-than-linear increase and are in good agreement with the NRQCD+CGC model, while predictions from PYTHIA8 fail to describe the data. Measuring Nψ(2S)/NJ/ψ even shows a more complex behavior, where the CGC alone fails. Considering dissociation mechanisms for charmonium can qualitatively explain the shape of the ratio.
Supported by BMFTR
Keywords: Charmonium; QCD; ALICE; Color Glass Condensate