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HK: Fachverband Physik der Hadronen und Kerne

HK 2: Heavy Ion Collision and QCD Phases I

HK 2.4: Vortrag

Montag, 14. März 2016, 15:00–15:15, S1/01 A01

Dileptons never die: measurement of virtual photons radiated from Au+Au collisions at E_beam=1.23 AGeV into HADES. — •Szymon Harabasz for the HADES collaboration — TU Darmstadt

Dileptons are a unique probe to direct study properties of hot and dense medium formed in heavy-ion collisions, thanks to their mean-free path much larger than the size of the fireball. Excess of the low-mass lepton pairs has been measured in heavy-ion collisions from SIS up to top RHIC energies. Substantial medium effects on light vector-mesons originate from their coupling to baryons and anti-baryons. In baryon-rich fireballs the low-mass excess is expected to be maximum.

This is the paramount topic in the experimental program conducted at SIS18 accelerator in GSI with the help of the High Acceptance Di-Electron Spectrometer. The strong non-linear system size dependence of the yield component exceeding the NN reference has been extracted from former C+C and Ar+KCl runs.

This contribution will present results of virtual photon production from high statistics Au+Au at E_beam = 1.23 AGeV data and confront them with the reference measured by HADES and with results of previous runs as well as with available model predictions. The integrated excess yield will be put in context of the dilepton excitation function measured by STAR.

This work has been supported by VH-NG-823, Helmholtz Alliance HA216/EMMI, GSI, HGS-HIRe and H-QM.