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_out2-R_side2) obtained from two-pion interferometry measurements in Au +Au (√{s_{N N} }=7.7 - 200 GeV ) and Pb +Pb (√{s_{N N} }=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 ,μ_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∼165 MeV and μ_B^cep∼95 MeV for the location of the critical end point. The critical exponents (ν ≈0.66 and γ ≈1.2 ) extracted via the same FSS analysis place this CEP in the 3D Ising model universality class.