Modification of the pi-omega-rho vertex in nuclear medium and its influence on the dilepton production rate in relativistic heavy-ion collisions

Abstract

In this PhD thesis we analyze the medium modification of the pi-omega-rho coupling and subsequently discuss its possible influence on the dilepton production rate in relativistic heavy-ion collisions. The first part of the thesis is devoted to the medium modifications of the Dalitz decays from the omega and rho mesons in nuclear matter. We use the relativistic field theory formalism describing modifications of the coupling by one-loop Feynman diagrams with nucleons and Delta(1232) isobars. We consider cases when the decaying particle is at rest or at motion with respect to the medium. We investigate the dependence of medium effects on the dilepton invariant mass and observe a sizeable increase of the effective coupling constants compared to their vacuum values. The effect grows with density. In the second part of the thesis we apply our model to evaluate the influence of the medium effects on the dilepton production from the Dalitz decays. In the calculations of the dilepton spectrum we use the model of the hydrodynamic expansion of the fire cylinder. In our comparison to the CERES dilepton data we take into account the experimental cuts. The medium modifications enhance the effect of the Dalitz decays. It is worth to point out that in the medium the rho decay due to the isospin degeneracy becomes as important as the omega decay. The main new and original results of the thesis are: 1. Significant in-medium increase of the pi-omega-rho coupling constant. 2. Large enhancement of the Dalitz decays from the omega and rho mesons in the range 0.2-0.6 GeV of the dilepton invariant mass.