Köln 2025 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 3: Heavy-Ion Collisions and QCD Phases I

HK 3.2: Talk

Monday, March 10, 2025, 15:15–15:30, HS 3 Chemie

Charmonium production at midrapidity using TRD-triggered data measured in ALICE — •Jinjoo Seo for the ALICE Germany collaboration — Heidelberg University, Heidelberg, Germany

Quarkonium production is considered one of the golden probes of quark-gluon plasma (QGP) formation in heavy-ion collisions. Quarkonium production in small collision systems, such as pp collisions, is also important for investigating production mechanisms and providing a reference for heavy-ion collisions. Charmonium, a bound state of charm and anti-charm quark pairs, has its production mechanism described by perturbative QCD for heavy quark production and non-perturbative QCD calculations for the formation of the bound state. Measurements of J/ψ and ψ(2S) cross sections in pp collisions are crucial for studying charmonium production mechanisms and testing different QCD-based model calculations. Especially, ψ(2S) production relative to J/ψ provides strong discriminating power among quarkonium production models. Thanks to the ALICE online single-electron triggers from the Transition Radiation Detector (TRD), the ψ(2S) signal can be extracted at midrapidity via the dielectron decay channel. In this contribution, the results on p_T-differential ψ(2S) production cross section at midrapidity with the TRD-triggered data measured in ALICE in pp collisions at √s = 13 TeV will be shown, along with those for J/ψ. In addition, the excited-to-ground state yield ratio (ψ(2S)-to-J/ψ) at midrapidity will be discussed. Results will be compared to measurements at forward rapidity and available model calculations.

Keywords: Charmonium