Heavy Ion Tea

Probing resonance matter with virtual photons

Tetyana Galatyuk (Goethe University)

Abstract: HADES has measured di-electron production in C+C, Ar+KCl, p+p, d+p and p+Nb collisions. The new HADES results confirm the previous DLS data, which could not satisfactorily be explained by various transport models for more than a decade. For a better understanding of the dielectron production in heavy ion collisions HADES has studied elementary NN interactions at E=1.25 GeV. For the first time, the electron pairs were reconstructed from quasi-free np sub-reactions by detecting the proton spectator from the deuteron breakup. A large difference in di-electron production in pp and np reactions measured at the same beam energy is observed. There is evidence that the appropriate superposition of the di-electron yields measured in pp and np (NN reference) can explain the CC dielectron yields in the mass region of 0.15<M/(GeV/c2 )<0.5. On the other hand, a direct comparison of the NN reference spectrum with the e+ e− invariant mass distribution measured in the heavier system ArKCl at 1.76 GeV/u shows an excess yield above the reference, which we attribute to radiation from resonance matter. Di-electron production in p+Nb at E=3.5GeV/u, was also recently measured with HADES to search for in-medium modifications of vector mesons at nuclear ground-state density. Results of the data analysis will be presented too.