Indications for a Critical End Point in the Phase Diagram for Hot and Dense Nuclear Matter

Excitation functions for the Gaussian emission source radii difference (R-out(2) - R-side(2)) obtained from two-pion interferometry measurements in Au + Au (root s(NN) = 7.7-200 GeV) and Pb + Pb (root s(NN) = 2.76 TeV) collisions are studied for a broad range of collision centralities. The observed nonmonotonic excitation functions validate the finite-size scaling patterns expected for the deconfinement phase transition and the critical end point (CEP), in the temperature versus baryon chemical potential (T, mu(B)) plane of the nuclear matter phase diagram. A finite-size scaling (FSS) analysis of these data suggests a second order phase transition with the estimates T-cep similar to 165 MeV and mu(cep)(B) similar to 95 MeV for the location of the critical end point. The critical exponents (nu approximate to 0.66 and gamma approximate to 1.2) extracted via the same FSS analysis place this CEP in the 3D Ising model universality class.