2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/176842Dilepton 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 photo-reactions on nucleons and nuclei. 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 SPS conditions. The resulting dimuon yield is in good agreement with the recent measurements reported by NA60.9 pages, 8 figuresNuclear TheoryHigh Energy Physics - Phenomenologytext