Time-Like Baryon Transitions in Hadroproduction

Abstract

The Dalitz decay of baryonic resonances (B $$\rightarrow $$ N $$e^+e^-$$ ) gives access to the time-like electromagnetic structure of baryonic transitions at small positive values of the squared four momentum transferred. Such processes were investigated by the HADES collaboration in elementary hadronic interactions. The Dalitz decay branching ratio of the $$\varDelta (1232)$$ resonance has been measured for the first time in pp reactions at 1.25 GeV beam energy. At higher energies, the $$e^+e^-$$ emission from baryonic decays is shown to be sensitive to transition form factors of the Vector Dominance Model type. Using a pion beam, Dalitz decays of baryonic resonances can be measured more directly. In addition, the simultaneous measurement of hadronic channels provides a new data base for baryon spectroscopy issues. Preliminary results of a test experiment in the N(1520) region are shown, together with prospects for higher resonance studies. A project of measuring hyperon Dalitz decays at GSI and later on at FAIR is also discussed. The study of Dalitz decays of baryon resonances and, in particular, the role of the $$\rho $$ meson brings useful constraints for the study of medium effects also investigated by the HADES collaboration in reactions with nuclei.