Thermal dilepton emission at low and intermediate energies

The systematic study of dilepton production in heavy-ion collisions across a large range of collision energies makes it possible to link experimental observables like yields and slopes of the spectra to features in the QCD phase diagram. As dileptons are emitted during the whole space-time evolution of the collision, the resulting spectra comprise several contributions from first-chance NN collisions, the hadronic freeze-out cocktail, but also thermal radiation which serves as messenger of the QCD matter properties inside the hot and dense medium. We couple in-medium thermal dilepton rates with a coarse-graining method of hadronic transport simulations to compute dilepton spectra at energies √(s_NN) ≤ 10 GeV, where hydrodynamic simulations may be less reliable. After checking the degree of thermalization of the system, local temperature, baryon and pion densities can be extracted in the nearly equilibrated parts of the fireball. This allows for the convolution of thermal rates with the space-time evolution of the medium. The results are discussed in the context of the excitation function of yields and slopes of the invariant-mass spectrum at different energies and compared to available experimental data.