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 ∼ (Tτ1/3)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 \( \sqrt{s_{NN}} \) = 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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Acknowledgments
We thank Jürgen Berges, Xiaojian Du, Charles Gale, Nicole Löher, Stephan Ochsenfeld, Jean-Francois Paquet and Klaus Reyers for their valuable discussions. OGM, PP and SS acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the CRC-TR 211 ‘Strong-interaction matter under extreme conditions’-project number 315477589 — TRR 211. AM acknowledges support by the DFG through Emmy Noether Programme (project number 496831614) and CRC 1225 ISOQUANT (project number 27381115). OGM and SS acknowledge also support by the German Bundesministerium für Bildung und Forschung (BMBF) through Grant No. 05P21PBCAA. The authors acknowledge computing time provided by the Paderborn Center for Parallel Computing (PC2) and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
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Garcia-Montero, O., Mazeliauskas, A., Plaschke, P. et al. Pre-equilibrium photons from the early stages of heavy-ion collisions. J. High Energ. Phys. 2024, 53 (2024). https://doi.org/10.1007/JHEP03(2024)053
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DOI: https://doi.org/10.1007/JHEP03(2024)053