Lepton pair spectroscopy with HADES at GSI

The High Acceptance DiElectron Spectrometer HADES is presently set up at GSI, Darmstadt, for the systematic study of medium modifications of hadron properties. Short lived hadrons will be produced in nuclear matter from normal up to medium baryon densities utilizing pion, proton and heavy ion induced reactions. Electron pair spectroscopy will be used to measure resonance widths and effective masses of vector mesons as well as transition formfactors of neutral mesons and baryon resonances in the low mass region M less than or equal to 1 GeV/c(2). The spectrometer is designed for an invariant mass resolution Delta Minv/Minv similar or equal to 1% (sigma), a large signal to background ratio, and a large acceptance Omega (pair) similar or equal to 40%.