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Elliptic flow of charm quarks produced in the early stage of pA collisions

Gabriele Parisi1,2,*, Fabrizio Murgana3,†, Vincenzo Greco1,2,‡, and Marco Ruggieri1,4,§

  • *Contact author: gabriele.parisi@dfa.unict.it
  • †Contact author: fabrizio.murgana@dfa.unict.it
  • ‡Contact author: greco@lns.infn.it
  • §Contact author: marco.ruggieri@dfa.unict.it
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Phys. Rev. D 113, 054033 – Published 23 March, 2026

DOI: https://doi.org/10.1103/9dgl-l9qs

Abstract

We investigate the buildup of elliptic flow of charm quarks produced in the early pre-equilibrium stage of high-energy proton-nucleus collisions. The initial stage is modeled within the color glass condensate framework as an evolving glasma, initialized through the McLerran-Venugopalan model. Subnucleonic fluctuations have been implemented as constituent-quark hotspots for both the proton and the nuclear participants. Charm quarks are propagated in the evolving non-Abelian background by solving the relativistic Wong equations for their coordinates, momenta, and color charges. First, we compute the nuclear modification factor of charm quarks, finding a slight migration towards higher pT states in agreement with previous results in the literature. Then, we focus on the azimuthal anisotropies acquired through the interaction with glasma fields. We find that glasma-induced momentum anisotropies are efficiently transmitted to heavy quarks within τ∼0.4  fm/c, leading to a sizeable charm-quark v2, with a magnitude that increases with the strength of the initial fields and with the number of nuclear participants. Remarkably, we show that the early stage contribution alone can account for a significant fraction of the experimentally observed J/ψ elliptic flow in p-Pb collisions, indicating that prehydrodynamic dynamics can play a non-negligible role in the final-state heavy-flavor collectivity, especially in small systems.

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Phys. Rev. D 113, 054033– Published 23 March, 2026
  • Received 23 January 2026
  • Accepted 5 March 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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