https://doi.org/10.1140/epjc/s10052-025-14072-6
Regular Article - Theoretical Physics
Effective temperatures of the QGP from thermal photon and dilepton production
1
Institute for Gravitational and Subatomic Physics, Utrecht University, 3584 CC, Utrecht, The Netherlands
2
Nikhef, Science Park 105, 1098 XG, Amsterdam, The Netherlands
3
Theoretical Physics Department, CERN, 1211, Geneva 23, Switzerland
4
European Organization for Nuclear Research (CERN), Geneva, Switzerland
5
Institute for Theoretical Physics, Utrecht University, 3584 CC, Utrecht, The Netherlands
Received:
17
January
2025
Accepted:
9
March
2025
Published online:
4
April
2025
Thermal electromagnetic radiation is emitted by the quark-gluon plasma (QGP) throughout its space-time evolution, with production rates that depend characteristically on the temperature. We study this temperature using thermal photons and dileptons using the Trajectum heavy ion code, which is constrained by Bayesian analysis. In addition we present the elliptic flow of both the thermal photons and thermal dileptons including systematic uncertainties corresponding to the model parameter uncertainty. We give a comprehensive overview of the resulting effective temperatures 
obtained from thermal photon transverse momentum and thermal dilepton invariant mass distributions, as well as the dependence of 
on various selection criteria of these probes. We conclude that the obtained from thermal photons is mostly insensitive to the temperature of the QGP with a value of 
–300 MeV depending on their transverse momentum, almost independent of collision centrality. Thermal dileptons are much better probes of the QGP temperature as they do not suffer from a blue shift as their invariant mass is used, allowing for a more precise constraint of the QGP temperature during different stages of the evolution of the system. By applying selection criteria on the dilepton transverse momentum and the invariant mass we are able to extract fluid temperatures on average times ranging from late emission 
to very early emissions 
Furthermore, we show how these selection criteria can be used to map the elliptic flow of the system all throughout its evolution.
© The Author(s) 2025
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
