Low mass dielectrons radiated off cold nuclear matter measured with HADES

Abstract

The High Acceptance DiElectron Spectrometer HADES [1] is installed at the Helmholtzzentrum f_s02r Schwerionenforschung (GSI) accelerator facility in Darmstadt. It investigates dielectron emission and strangeness production in the 1-3 AGeV regime. A recent experiment series focusses on medium-modifications of light vector mesons in cold nuclear matter. In two runs, p_s16p and p_s16Nb reactions were investigated at 3.5 GeV beam energy_s19 about 9·109 events have been registered. In contrast to other experiments the high acceptance of the HADES allows for a detailed analysis of electron pairs with low momenta relative to nuclear matter, where modifications of the spectral functions of vector mesons are predicted to be most prominent. Comparing these low momentum electron pairs to the reference measurement in the elementary p_s16p reaction, we find in fact a strong modification of the spectral distribution in the whole vector meson region.