Resonant dileptons as a thermometer for the QCD transition temperature

The transverse mass distribution of dileptons in the rho-omega peak is sensitive to the transition from the hadronic to the quark-gluon phase expected in ultra-relativistic nuclear collisions. The authors calculate thermal production rates for lepton pairs from this resonance in the course of a sufficiently high-energy collision. They assume thermal and chemical equilibrium throughout the collision, and focus on the baryon-free central rapidity region. Two different equations of state, one with a strong first-order deconfinement phase transition and one with a chiral melting transition, are used to represent the range of possibilities. They consider transition temperatures between 150 and 200 MeV. The dilepton signal is calculated based on a boost-invariant longitudinal expansion. They study the effects of transverse expansion using a one-dimensional fluid-dynamical description as an approximation. The authors then fit the transverse mass distributions to thermal distributions to simulate the experimental procedure. They find that the fitting temperatures are strongly correlated to the assumed transition temperatures, and thus, if a transition is present, its temperature can be measured by the dilepton signal from the rho-omega peak under the above assumptions