Münster 2017 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 3: Heavy Ion Collisions and QCD Phases II

HK 3.1: Gruppenbericht

Montag, 27. März 2017, 16:45–17:15, F 3

Electromagnetic probes of hot and dense matter produced in Au+Au collisions at E_beam=1.23A GeV. — •Szymon Harabasz for the HADES collaboration — TU Darmstadt

Properties of hot and dense QCD medium formed in heavy-ion collisions can be extracted directly from its emissivity in electromagnetic sector. Excess of the low-mass lepton pairs has been measured in such collisions in energy regimes from SIS18 up to top RHIC. Substantial medium effects on light vector mesons is attributed to their coupling to baryons and anti-baryons.

HADES has contributed to this study in moderate temperature but high density region of the QCD phase diagram by measuring lepton pairs production in N+N, N+A, A+A, π+N and π+A at the SIS18 accelerator in GSI. The strong non-linear system size dependence of the excess yield over the experimentally established "cocktail" has been previously extracted from the C+C and Ar+KCl runs.

In this presentation an overview of the results on electromagnetic probes from high statistics Au+Au at E_beam = 1.23A GeV data will be provided. Virtual photon spectra will be confronted with results of other experiments as well as with available model predictions. The understanding of the emerging physical implications can be refined by looking at direct photon production and virtual photon flow. EM transitions of baryonic resonances measured directly in pion-induced reactions are pivotal input to model calculations.

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