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

Abstract

We investigate the build-up 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 $p_T$ 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 $\tau \sim 0.4fm/c$, leading to a sizeable charm-quark $v_2$, 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 $J/\psi$ elliptic flow in p-Pb collisions, indicating that pre-hydrodynamic dynamics can play a non-negligible role in the final-state heavy-flavor collectivity, especially in small systems.

12 pages, 9 figures. v2: added reference to Zenodo repository, minor revisions to match the version published in Phys. Rev. D

References in corpus (14)

• The Color Glass Condensate
• Some Features of the Glasma
• Analysis of combined HERA data in the Impact-Parameter dependent Saturation model
• Running the gamut of high energy nuclear collisions
• Simulating jets and heavy quarks in the Glasma using the colored particle-in-cell method
• Small x physics and RHIC data
• Ballistic diffusion of heavy quarks in the early stage of relativistic heavy ion collisions at RHIC and LHC
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• Physical characteristics of glasma from the earliest stage of relativistic heavy ion collisions
• Energy Loss Versus Energy Gain of Heavy Quarks in a Hot Medium
• The energy-momentum tensor at the earliest stage of relativistic heavy ion collisions
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