title: Comprehensive interpretation of thermal dileptons measured at the CERN super proton synchrotron.
abstract: Employing thermal dilepton rates based on a medium-modified electromagnetic correlation function we show that recent dimuon spectra of the NA60 Collaboration in central In-In collisions at the CERN-SPS can be understood in terms of radiation from a hot and dense hadronic medium. Earlier calculated in-medium rho-meson spectral functions provide an accurate description of the data up to dimuon invariant masses of about M approximately or equal to 0.9 GeV, with good sensitivity to the predicted rho-meson line shape, identifying baryon-induced modifications as the prevalent ones. A reliable evaluation of the contribution enables the study of further medium effects: at masses M>0.9 GeV, 4-pion type annihilation accounts for the experimentally observed excess (possibly augmented by effects of "chiral mixing"), while predictions for thermal emission from in-medium omega and phi mesons may be tested in the future.
authors.affiliation: Cyclotron Institute and Physics Department, Texas A & M University, College Station, Texas, 77843-3366 USA.
authors.forename: Hendrik
authors.initials: H
authors.lastname: van Hees
authors.forename: Ralf
authors.initials: R
authors.lastname: Rapp