Mesonic sources of dileptons in ultrarelativistic nuclear collisions

In this work thermal dilepton production from a hot medium created in heavy ion collision is studied. Using an effective Lagrangian technique for particle decays and annihilations, a complete method for calculation of the lepton pair production rate is developed. The importance of axial vector meson contributions to the dilepton spectrum is analyzed. Different effective Lagrangians for the a1rhopi interaction are considered, and a new form of b1o(&phis;)pi effective Lagrangian is introduced.A systematic study of light meson contributions is performed. The most significant decay and reaction contributions are calculated and summed for low and intermediate invariant mass dileptons. The calculated dilepton rate is compared to that obtained using spectral functions extracted from data, and it is shown that the chosen set of mesonic reactions and decays accounts for all significant contributions to the thermal dilepton emission.A hydrodynamic approach to the space-time evolution of the hot medium formed as a result of a central heavy ion collision at ultra-relativistic energies is considered. A theoretical curve of intermediate invariant mass dilepton spectrum is computed and compared to the NA50 data from central Pb(158 AGeV)+Pb collisions. Experimental acceptance cuts are accounted for. Drell-Yan processes are considered as well. We find that our thermal dileptons account for the intermediate mass excess observed by the NA50 Collaboration. We see no need to invoke charm enhancement. Predictions for the future experiments at RHIC and are made