Excitation functions for the Gaussian emission source radii difference ($R_{\text{out}}^2-R_{\text{side}}^2$) obtained from two-pion interferometry measurements in $\mathrm{Au}+\mathrm{Au}$ ($\sqrt{s_{NN}}=7.7–200\mathrm{GeV}$) and $\mathrm{Pb}+\mathrm{Pb}$ ($\sqrt{s_{NN}}=2.76\mathrm{TeV}$) 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 $T^{\mathrm{cep}}\sim 165\mathrm{MeV}$ and ${\mu }_B^{\mathrm{cep}}\sim 95\mathrm{MeV}$ for the location of the critical end point. The critical exponents ($\nu \approx 0.66$ and $\gamma \approx 1.2$) extracted via the same FSS analysis place this CEP in the 3D Ising model universality class.

• Received 15 December 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.142301