Acta Phys. Hung. A 22/3–4 (2005) 239–244 HEAVY ION PHYSICS Baryonic Channels of Dilepton Production Mikl´osZ´ et´ enyi and Gy¨orgy Wolf MTA KFKI, Research Institute for Particle and Nuclear Physics H-1525 Budapest, Hungary Received 27 September 2004 Abstract. A calculation of the Dalitz-decay width of baryon resonances is presented and applied to dilepton production in proton–proton collisions in the BEVALAC/SIS energy range. The results indicate, that for these energies the contribution of Dalitz decay of higher baryon resonances (i.e. other that the Δ(1232)) are negligible. Keywords: dilepton production, proton–proton collisions PACS: 13.75.Cs, 13.30.Ce, 13.40.Hq, 14.20.Gk 1. Introduction Dilepton (electron–positron pair) production is a favorable probe of the hot and dense matter formed in heavy-ion collisions, because these particles do not suffer strong final state interactions in the medium, and, therefore, carry information about the conditions at their creation time. Specifically, the neutral vector mesons ρ 0 , ω and φ decay directly to a dilepton, and the invariant mass of this dilepton gives the mass of the decaying meson. Therefore the in-medium spectral function of the neutral vector mesons might be studied via the dilepton invariant mass spectrum of heavy-ion collisions. In addition to the vector meson decays, other processes contribute to the dilepton spectrum as a background. These are the Dalitz decay of mesons π 0 → γ e + e - , η → γ e + e - , ω → π 0 e + e - , and baryon resonances R → N e + e - , pion annihilation π + π - → e + e - and bremsstrahlung in pn collisions. The above elementary processes of dilepton production are not very well under- stood theoretically, and, even for proton–proton collisions, various model calcula- tions of dilepton production exist with different elementary channels and parameter sets [1]. The main difference in the production channels of these models arise from different factorizations of Feynman diagrams of production processes, and different separation of resonant and non-resonant contributions. Traditionally, Dalitz de- cays of baryon resonances other than the Δ(1232) are excluded from the models, except for some contributions of the N(1520) in [1]. However, these channels may 1219-7580/ $ 20.00 c  2005 Akad´ emiai Kiad´o, Budapest