Experimental and Theoretical Studies: Analysis of Low-mass Dilepton Enhancement in 200 GeV Au+Au Collisions at RHIC (thesis)

In case of an UA(1) symmetry restoration in a hot and dense hadronic matter, the mass of the produced hadrons and mesons can significantly change, and their production cross-section can also be modified. In this M.Sc. Thesis I search for the signature of an eta' enhancement in the PHENIX dilepton spectrum in 200 GeV Au+Au collisions, which has a significant enhancement in the low-mass region, e.g. in the (0.1-1.0) GeV invariant electron-positron mass range. This is also the region of the eta' meson's Dalitz-decay (eta'->ee gamma), so the eta' enhancement might be responsible for at least a part of the excess. Other mesons' (other) properties can also be changed in the hot, dense medium, but in this thesis I focus on the mass modification of the eta' meson. To explore the role of eta', I used EXODUS simulations to generate different dilepton spectra, corresponding to different eta' properties. The conclusion here was that the excess can not be described with just the eta' mass modification, but the agreement with data has been improved significantly. Another idea which might brings us closer to understand the excess is to examine the radial flow of the mesons, which was not included in the original PHENIX analysis. Radial flow is important in the low-pT range, where it describes the particles' spectra well: just in the region where the dilepton spectrum has the most contributions from. Thus examining the effect of the radial flow seems to be inevitable, as it might be responsible for certain parts of the excess. The results summarized here are work in progress, obtained with the framework of the PHENIX Collaboration at RHIC.