Enhanced dilepton emission from a phase transition in dense matter

Abstract It is demonstrated that the presence of a phase transition in heavy ion collisions, at beam energies that probe dense QCD matter, leads to a significant enhancement of the dilepton yield at low invariant mass and low beam energies per produced pion due to the extended emission time.
In addition, the temperature of low mass dileptons shows a modest decrease due to the mixed phase.
The emission of dileptons in the SIS18--SIS100 beam energies range is studied by augmenting the UrQMD transport model with a realistic density dependent equation of state, as well as two different phase transitions. This is achieved by extending the molecular dynamics interaction part of the UrQMD model to a density dependent interaction potential with a high density minimum leading to a phase transition and metastable coexisting high density states.
Together with a high precision measurement these simulations will be able to constrain the existence of a phase transition in QCD up to densities of several times nuclear saturation density.