Learning from decays
Heavy ion collisions at (ultra-) relativistic energies are a unique tool to create and study QCD matter under extreme conditions. Among the many possibilities available for such investigations, photons and dileptons play a special role.
Once produced by a particle decay, they effectively decouple from the strongly interacting system and carry important information about its structure to the detectors. However, the dilepton and photon properties recorded in experiments represent the space-time integral of photons emitted throughout the evolution of the reaction - from the initial collisions of the nuclei to the electromagnetic decays of the long-lived particles. Proper disentanglement of the various contributions to the total spectrum is an important prerequisite for studying QCD matter under extreme conditions with such penetrating probes.