The HADES Pion Beam Facility

The quest for unraveling the origin of confinement and spontaneous breaking of chiral symmetry have been the driving force for hadron and nuclear matter physics over the last two decades. Both processes are responsible for the generation of mass of all hadronic matter around us [1]. The High Acceptance DiElectron Spectrometer (www-hades.gsi.de) has been designed and put into operation in 2003 to search for signatures of a (partial) restoration of chiral symmetry, then thought to be observable by measuring in-medium (shift of pole) masses of the vector mesons [2, 3]. Electromagnetic decays of the low-mass vector mesons, in particular the ρ meson, represent a formidable choice since they can decay exclusively into a pair of leptons. Hence, in-medium decays become observable by reconstructing the invariant mass of the lepton pairs recorded in the spectrometer.