Speaker
Description
Dileptons are a unique probe to study microscopic properties of nuclear matter under extreme
conditions of temperature and density achieved in heavy-ion collisions. The low-mass excess radiation
(above cocktail) observed from SIS to top RHIC energies is well understood theoretically in terms of
strict VMD assuming strong broadening of the in-medium rho spectral function. This broadening is
linked to the coupling of vector mesons to baryons and anti-baryons and is expected to be maximal in
baryon-rich medium as formed at lowest beam energies.
This is the paramount topic of the experimental program of HADES conducted at SIS18 accelerator
in GSI. Strong, non-linear system size dependence of the integrated yield above the NN reference
has been extracted from former C+C and Ar+KCl runs [1].
This contribution will present results on virtual photon production from high statistics Au+Au at
$𝐸_{\textrm{beam}}$ = 1.23A$~$GeV data and confront them with the reference measured by HADES as well as with
available model predictions. The integrated excess yield will be put in context of the dilepton
excitation function measured in RHIC beam energy scan.
[1] G. Agakishiev et al. [HADES Collaboration], Phys. Rev. C 84 (2011) 014902
This work has been supported by TU Darmstadt: VH-NG-823, Helmholtz Alliance HA216/EMMI
and GSI.
