Thermal dimuon yields: Comparison with NA60 results at 158 GeV/nucleon

Dilepton emission rates from a hadronic gas at finite temperature and baryon density are completely constrained by broken chiral symmetry in a density expansion. The rates can be expressed in terms of vacuum correlations which are measured in e+e- annihilation, τ decays, and photoreactions on nucleons and nuclei [1-3]. In this paper, the theoretical results are summarized and the total dimuon yield is calculated by integrating the dimuon rates over the space-time history of a fireball based on hydrodynamic calculations with CERN Super Proton Synchrotron (SPS) conditions. We compare the resulting dimuon yield with the recent measurements reported by NA60 [4].