Pre-equilibrium photons from the early stages of heavy-ion collisions

2023/08/18 by Oscar Garcia-Montero, Aleksas Mazeliauskas, Garcia-Montero, Oscar +5 · 6 citations
Physics and Astronomy · #Cosmology and Gravitation Theories #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Nuclear Theory (nucl-th) #Quantum Chromodynamics and Particle Interactions

paper · pdf · doi:10.48550/arxiv.2308.09747

openalex publication_date 2023/08/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01

Abstract

We use QCD kinetic theory to compute photon production in the chemically equilibrating Quark-Gluon Plasma created in the early stages of high-energy heavy-ion collisions. We do a detailed comparison of pre-equilibrium photon rates to the thermal photon production. We show that the photon spectrum radiated from a hydrodynamic attractor evolution satisfies a simple scaling form in terms of the specific shear viscosity η/s and entropy density dS/dζ∼ \scriptstyle (Tτ^1/3)^3/2_∞. We confirm the analytical predictions with numerical kinetic theory simulations. We use the extracted scaling function to compute the pre-equilibrium photon contribution in √s_NN=2.76 TeV 0-20% PbPb collisions. We demonstrate that our matching procedure allows for a smooth switching from pre-equilibrium kinetic to thermal hydrodynamic photon production. Finally, our publicly available implementation can be straightforwardly added to existing heavy ion models.

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