Searching for the QCD Critical Point with Net-Proton Number Fluctuations

Abstract

PACS 25.75.Nq, 25.75.Gz Net-proton number fluctuations can be measured experimentally and hence provide a source of important information about the matter created during relativistic heavy ion collisions. Particularly, they may give us clues about the conjectured QCD critical point. In this work the beam-energy dependence of ratios of the first four cumulants of the net-proton number is discussed. These quantities are calculated using a phenomenologically motivated model in which critical mode fluctuations couple to protons and anti-protons. Our model qualitatively captures both the monotonic behavior of the lowest-order ratio as well as the non-monotonic behavior of higher-order ratios, as seen in the experimental data from the STAR Collaboration. We also discuss the dependence of our results on the coupling strength and the location of the critical point. K e y w o r d s: net-proton number fluctuations, QCD critical point, heavy-ion collisions