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  • Open Access

Electromagnetic probes as signatures for a first-order QCD phase transition

Mohamad Lukman Aidid Mohd Yusoff, Norhasliza Yusof*, and Hasan Abu Kassim

Jan Steinheimer

Marcus Bleicher

Apiwit Kittiratpattana, Ayut Limphirat, and Christoph Herold†

  • Center of Excellence in High Energy Physics and Astrophysics, School of Physics, Suranaree University of Technology, University Avenue 111, Nakhon Ratchasima 30000, Thailand

  • *Contact author: norhaslizay@um.edu.my
  • †Contact author: herold@g.sut.ac.th
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Phys. Rev. C 113, 014915 – Published 29 January, 2026

DOI: https://doi.org/10.1103/9qvy-f1gf

Abstract

We investigate dimuon production in the context of a first-order phase transition in QCD matter using a chiral fluid dynamics model. This approach incorporates nonequilibrium effects such as entropy production and reheating, which emerge during the dynamical evolution through a first-order phase transition. By comparing equilibrium and nonequilibrium scenarios across a range of beam energies (sNN=2.2–6.2 GeV), we analyze the resulting invariant mass spectra. Our results reveal a substantial enhancement of dilepton yields in the nonequilibrium scenario, particularly pronounced at lower beam energies, where reheating leads to a prolonged lifetime of the fireball and increased emission. The enhancement persists even after normalizing to pion multiplicities, indicating sensitivity beyond effects of entropy production.

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References (46)

  1. M. S. Abdallah, et al. (STAR Collaboration), Cumulants and correlation functions of net-proton, proton, and antiproton multiplicity distributions in Au+Au collisions at energies available at the BNL Relativistic Heavy Ion Collider, Phys. Rev. C 104, 024902 (2021).
  2. B. Friman, F. Karsch, K. Redlich, and V. Skokov, Fluctuations as probe of the QCD phase transition and freeze-out in heavy ion collisions at LHC and RHIC, Eur. Phys. J. C 71, 1694 (2011).
  3. Y. Aoki, G. Endrodi, Z. Fodor, S. D. Katz, and K. K. Szabo, The order of the quantum chromodynamics transition predicted by the standard model of particle physics, Nature (London) 443, 675 (2006).
  4. Y. Aoki, Z. Fodor, S. D. Katz, and K. K. Szabo, The QCD transition temperature: Results with physical masses in the continuum limit, Phys. Lett. B 643, 46 (2006).
  5. Y. Aoki, S. Borsányi, S. Dürr, Z. Fodor, S. D. Katz, et al., The QCD transition temperature: Results with physical masses in the continuum limit II., J. High Energy Phys. 06 (2009) 088.
  6. S. Borsanyi, et al. (Wuppertal-Budapest Collaboration), Is there still any Tc mystery in lattice QCD? Results with physical masses in the continuum limit III, J. High Energy Phys. 09 (2010) 073.
  7. C. S. Fischer, J. Luecker, and C. A. Welzbacher, Phase structure of three and four flavor QCD, Phys. Rev. D 90, 034022 (2014).
  8. P. Isserstedt, M. Buballa, C. S. Fischer, and P. J. Gunkel, Baryon number fluctuations in the QCD phase diagram from Dyson-Schwinger equations, Phys. Rev. D 100, 074011 (2019).
  9. F. Gao and J. M. Pawlowski, Chiral phase structure and critical end point in QCD, Phys. Lett. B 820, 136584 (2021).
  10. J. Adamczewski-Musch, et al., Proton-number fluctuations in sNN =2.4 GeV Au + Au collisions studied with the High-Acceptance DiElectron Spectrometer (HADES), Phys. Rev. C 102, 024914 (2020).
  11. M. S. Abdallah, et al. (STAR Collaboration), Measurement of the sixth-order cumulant of net-proton multiplicity distributions in Au+Au collisions at sNN= 27, 54.4, and 200 GeV at RHIC, Phys. Rev. Lett. 127, 262301 (2021) [ 134, 139903(E) (2025)].
  12. B. Berdnikov and K. Rajagopal, Slowing out-of-equilibrium near the QCD critical point, Phys. Rev. D 61, 105017 (2000).
  13. C. Athanasiou, K. Rajagopal, and M. Stephanov, Using higher moments of fluctuations and their ratios in the search for the QCD critical point, Phys. Rev. D 82, 074008 (2010).
  14. M. Stephanov, On the sign of Kurtosis near the QCD critical point, Phys. Rev. Lett. 107, 052301 (2011).
  15. M. Nahrgang, S. Leupold, C. Herold, and M. Bleicher, Nonequilibrium chiral fluid dynamics including dissipation and noise, Phys. Rev. C 84, 024912 (2011).
  16. S. Mukherjee, R. Venugopalan, and Y. Yin, Real time evolution of non-Gaussian cumulants in the QCD critical regime, Phys. Rev. C 92, 034912 (2015).
  17. L. Jiang, P. Li, and H. Song, Correlated fluctuations near the QCD critical point, Phys. Rev. C 94, 024918 (2016).
  18. C. Herold, M. Nahrgang, Y. Yan, and C. Kobdaj, Dynamical net-proton fluctuations near a QCD critical point, Phys. Rev. C 93, 021902 (2016).
  19. C. Herold, M. Bleicher, M. Nahrgang, J. Steinheimer, A. Limphirat, C. Kobdaj, and Y. Yan, Broadening of the chiral critical region in a hydrodynamically expanding medium, Eur. Phys. J. A 54, 19 (2018).
  20. M. Stephanov and Y. Yin, Hydrodynamics with parametric slowing down and fluctuations near the critical point, Phys. Rev. D 98, 036006 (2018).
  21. M. Stephanov and Y. Yin, Hydrodynamics and critical slowing down, Nucl. Phys. A 967, 876 (2017).
  22. M. Nahrgang, M. Bluhm, T. Schaefer, and S. A. Bass, Diffusive dynamics of critical fluctuations near the QCD critical point, Phys. Rev. D 99, 116015 (2019).
  23. M. Nahrgang and M. Bluhm, Modeling the diffusive dynamics of critical fluctuations near the QCD critical point, Phys. Rev. D 102, 094017 (2020).
  24. L. Du, U. Heinz, K. Rajagopal, and Y. Yin, Fluctuation dynamics near the QCD critical point, Phys. Rev. C 102, 054911 (2020).
  25. R. Rapp and H. van Hees, Thermal dileptons as fireball thermometer and chronometer, Phys. Lett. B 753, 586 (2016).
  26. F. Seck, T. Galatyuk, A. Mukherjee, R. Rapp, J. Steinheimer, J. Stroth, and M. Wiest, Dilepton signature of a first-order phase transition, Phys. Rev. C 106, 014904 (2022).
  27. O. Savchuk, A. Motornenko, J. Steinheimer, V. Vovchenko, M. Bleicher, M. Gorenstein, and T. Galatyuk, Enhanced dilepton emission from a phase transition in dense matter, J. Phys. G 50, 125104 (2023).
  28. C. Herold, A. Kittiratpattana, C. Kobdaj, A. Limphirat, Y. Yan, M. Nahrgang, J. Steinheimer, and M. Bleicher, Entropy production and reheating at the chiral phase transition, Phys. Lett. B 790, 557 (2019).
  29. C. Herold, A. Limphirat, P. Saikham, M. Nahrgang, T. Reichert, and M. Bleicher, Net-proton number cumulant ratios as a function of beam energy from an expanding nonequilibrium chiral fluid, Phys. Rev. C 106, 024901 (2022).
  30. O. Garcia-Montero, P. Plaschke, and S. Schlichting, Scaling of pre-equilibrium dilepton production in QCD kinetic theory, Phys. Rev. D 111, 034036 (2025).
  31. M. Coquet, X. Du, J.-Y. Ollitrault, S. Schlichting, and M. Winn, Intermediate mass dileptons as pre-equilibrium probes in heavy ion collisions, Phys. Lett. B 821, 136626 (2021).
  32. X.-Y. Wu, L. Du, C. Gale, and S. Jeon, Probing the equilibration of the QCD matter created in heavy-ion collisions with dileptons, Phys. Rev. C 110, 054904 (2024).
  33. J. Churchill, L. Du, C. Gale, G. Jackson, and S. Jeon, Virtual photons shed light on the early temperature of dense QCD matter, Phys. Rev. Lett. 132, 172301 (2024).
  34. L. Du, Multimessenger study of baryon-charged QCD matter in heavy-ion collisions, Phys. Lett. B 861, 139270 (2025).
  35. O. Massen, G. Nijs, M. Sas, W. van der Schee, and R. Snellings, Effective temperatures of the QGP from thermal photon and dilepton production, Eur. Phys. J. C 85, 388 (2025).
  36. J. Cleymans, J. Fingberg, and K. Redlich, Transverse momentum distribution of dileptons in different scenarios for the QCD phase transition, Phys. Rev. D 35, 2153 (1987).
  37. H. van Hees and R. Rapp, Dilepton radiation at the CERN Super Proton Synchrotron, Nucl. Phys. A 806, 339 (2008).
  38. M. Laine, NLO thermal dilepton rate at non-zero momentum, J. High Energy Phys. 11 (2013) 120.
  39. J. Ghiglieri and G. D. Moore, Low mass thermal dilepton production at NLO in a weakly coupled quark-gluon plasma, J. High Energy Phys. 12 (2014) 029.
  40. Y. Burnier and C. Gastaldi, Contribution of next-to-leading order and Landau-Pomeranchuk-Migdal corrections to thermal dilepton emission in heavy-ion collisions, Phys. Rev. C 93, 044902 (2016).
  41. J. Churchill, L. Du, C. Gale, G. Jackson, and S. Jeon, Dilepton production at next-to-leading order and intermediate invariant-mass observables, Phys. Rev. C 109, 044915 (2024).
  42. H. B. Meyer, M. Cè, T. Harris, A. Krasniqi, and C. Török, Photon and dilepton production rate in the quark-gluon plasma from lattice QCD, PoS LATTICE2022, 186 (2023).
  43. A. H. Taub, Relativistic Rankine-Hugoniot equations, Phys. Rev. 74, 328 (1948).
  44. K. S. Thorne, Relativistic shocks: The Taub Adiabat, Astrophys. J. 179, 897 (1973).
  45. T. Bumnedpan, J. Steinheimer, M. Bleicher, A. Limphirat, and C. Herold, Enhanced pion-to-proton ratio at the onset of the QCD phase transition, Phys. Lett. B 835, 137537 (2022).
  46. M. S. Abdallah,, et al. (STAR), Disappearance of partonic collectivity in SNN=3 GeV Au+Au collisions at RHIC, Phys. Lett. B 827, 137003 (2022).

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Phys. Rev. C 113, 014915– Published 29 January, 2026
  • Received 9 October 2025
  • Accepted 10 December 2025
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