The ρ meson in hot hadron matter and low mass dilepton spectra

The structure of the one loop self-energy graphs of the ρ meson is analyzed in the real time formulation of thermal field theory. The modified spectral function of the ρ meson in hot hadronic matter leads to a large enhancement of lepton pair production below the bare peak of the ρ. It has been shown that the effective temperature extracted from the inverse slope of the transverse mass distributions for various invariant mass (M) windows of the pair can be used as an efficient tool to characterize different phases of the evolving matter.