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HK: Fachverband Hadronen und Kerne
HK 69: Hadron Structure and Spectroscopy I
HK 69.1: Eingeladener Gruppenbericht
Donnerstag, 19. März 2009, 16:30–17:00, H-ZO 20
Probing resonance matter with virtual photons — •Tetyana Galatyuk — Institut für Kernphysik, Goethe-Universität, Frankfurt am Main, Germany
The HADES experiment, installed at GSI, Darmstadt, has measured di-electron production in 12C+12C, 40Ar+39KCl, p+p, d+p and p+93Nb collisions. The results of the 12C+12C data taken at a kinetic beam energy of 1 GeV/u and 2 GeV/u suggest that a substantial fraction of electron pairs with masses larger than 0.15 GeV/c2 stem from Dalitz decays of baryonic resonances. For a better understanding of the dielectron production in heavy ion collisions HADES has therefore studied elementary p+p and d+p interactions at Ekin = 1.25 GeV/u. The main interests here are the investigation of iso-spin effects in baryonic resonance excitation and the off-shell production of vector mesons. We observe indeed a large difference in dielectron production in p+p and d+p reactions measured at the same beam energy.
The production of e+e− pairs in 40Ar+39KCl collisions at a beam energy of 1.75 GeV/u was measured in August 2005. Results of these data will be discussed and compared to results of the 12C+12C runs.
In May 2007 data with high statistics were taken for p+p interactions at Ekin = 3.5 GeV. We use this data to study ω meson production, in particular its free line shape. Precise ω reconstruction in this reactions will serve as a reference for studies of the ω line shape in p+93Nb reactions. Dielectron production in p+93Nb, was recently measured with HADES to search for medium effects at nuclear ground state density. Preliminary results of the data analysis will also be reported.