Hadronic entropy enhancement and low density QGP

Recent studies show that for central collisions the rise in the incident energy from AGS to RHIC decreases the value of the chemical potential in the hadron-QGP phase diagram. Thus, the formation of QGP at RHIC energies in central collisions may be expected to occur at very small values of the chemical potential. Using many different relativistic mean-field hadronic models (RMF) at this regime we show that the critical temperature for the hadron-QGP transition is hadronic model independent. We have traced back the reason for this and conclude that it comes from the fact that the QGP entropy is much larger than the hadronic entropy obtained in all the RMF models. We also find that almost all of these models present a strong entropy enhancement in the hadronic sector coming from the baryonic phase transition to a nucleon–antinucleon plasma. This result is in agreement with the recent data obtained in the STAR collaboration at RHIC where a rich proton–antiproton matter was found.