https://doi.org/10.1051/epjconf/202429607009
Understanding the properties of the fireball with the polarization signature of thermal dileptons
1 Technische Universität Darmstadt, 64289 Darmstadt, Germany
2 GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany
3 Institut für Theoretische Physik, Goethe-Universität Frankfurt, 60438 Frankfurt (Main), Germany
4 Helmholtz Research Academy Hesse for FAIR, Campus Frankfurt, 60438 Frankfurt (Main), Germany
5 Theoretical Physics Department, CERN, 1211 Geneva 23, Switzerland
6 Texas A&M University, College Station, TX 77843-3366, USA
* e-mail: f.seck@gsi.de
Published online: 26 June 2024
Multi-differential measurements of dilepton spectra serve as a unique tool to characterize the properties of matter in the interior of the hot and dense fireball created in heavy-ion collisions. An important property of virtual photons is their spin polarization defined in the rest frame of the virtual photon with respect to a chosen quantization axis. Microscopic calculations of in-medium electromagnetic spectral functions have mostly focused on integrated yields which are proportional to the sum of the longitudinal and transverse components of the virtual photon’s self-energy, while photon polarization results from the difference of these components. As the processes that drive the medium effects in the spectral function change with invariant mass and momentum, this becomes a powerful tool for studying the medium composition. We present the polarization observables of thermal virtual photons as a function of mass and momentum and confront the results with existing measurements from HADES and NA60.
© The Authors, published by EDP Sciences, 2024
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
