Exploring the partonic collectivity in small systems at energies available at the CERN Large Hadron Collider

Journal Article · Sun Feb 01 00:00:00 EST 2026 · Physical Review C

DOI:https://doi.org/10.1103/n22l-1gdb· OSTI ID:3025141

Wang, Yuanyuan; Wang, Yili; Zhao, Wenbin; Song, Huichao

Using the Hydro-Coal-Frag model that combines hydrodynamics at low pT, quark coalescence at intermediate pT, and the LBT transport model at high pT, we study the spectra and elliptic flow of identified hadrons in high multiplicity p–Pb and p–p collisions at the CERN Large Hadron Collider (LHC). In p–Pb collisions, the Hydro-Coal-Frag model gives a good description of the differential elliptic flow over the pT range from 0 to 6 GeV and the approximate number of constituent quark (NCQ) scaling at intermediate pT. Although the Hydro-Coal-Frag model can also roughly describe the elliptic flow in high multiplicity p–p collisions with the quark coalescence process, the larger contribution from the string fragmentations leads to a notable violation of the NCQ scaling of v2 at intermediate pT as observed in the experiment. Comparison runs of the Hydro-Frag model without the coalescence process demonstrate that regardless the parameter adjustments, the Hydro-Frag model cannot simultaneously describe the pT spectra and the elliptic flow of identified hadrons in either p–Pb collisions or p–p collisions. The calculations in this paper thus provide support for the existence of partonic degrees of freedom and the possible formation of the QGP in the small systems created at the LHC.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: US Department of Energy; USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 3025141
• Journal Information: Physical Review C, Journal Name: Physical Review C Journal Issue: 2 Vol. 113
• Country of Publication: United States
• Language: English