Net-proton measurements at RHIC and the QCD phase diagram

Two measurements related to the proton and anti-proton production near midrapidity in center of mass energies of 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au+Au collisions using the STAR detector at the Relativistic Heavy Ion Collider (RHIC) are discussed. At intermediate impact parameters the slope parameter of the directed flow versus rapidity (dv1/dy) for the net-protons shows a non-monotonic variation as a function of the beam energy. This non-monotonic variation is characterized by the presence of a minimum in dv1/dy between 11.5 and 19.6 GeV and a change in the sign of dv1/dy twice between 7.7 and 39 GeV. At small impact parameters the product of the moments of net-proton distribution, kurtosis x variance and skewness x standard deviation are observed to be significantly below the corresponding measurements at large impact parameter collisions for 19.6 and 27 GeV. The kurtosis x variance and skewness x standard deviation at these beam energies deviate from the expectations from Poisson statistics and that from a Hadron Resonance Gas model. Both these measurements have implications towards the understanding of the QCD phase structures, the first order phase transition and the critical point in the high baryonic chemical potential region of the phase diagram.