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Comprehensive Interpretation of Thermal Dileptons at the SPS

Hendrik van Hees·Ralf Rapp
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Abstract

Employing thermal dilepton rates based on medium-modified electromagnetic correlation functions 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 ρ-meson spectral functions, as following from hadronic many-body theory, provide an accurate description of the data up to dimuon invariant masses of about M\simeq 0.9 GeV, with good sensitivity to details of the predicted ρ-meson line shape. This, in particular, identifies baryon-induced effects as the prevalent ones. We show that a reliable description of the ρcontribution opens the possibility to study further medium effects: at higher masses (M \simeq 0.9-1.5 GeV) 4-pion type annihilation is required to account for the experimentally observed excess indicating precursor effects of chiral symmetry restoration (``chiral mixing''), while remaining structures in the ωand ϕregion are suggestive for modifications in their line shapes as well.

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Hendrik van Hees, Ralf Rapp. 2006-08-28. Comprehensive Interpretation of Thermal Dileptons at the SPS. https://doi.org/10.1103/physrevlett.97.102301

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