Large baryon density fluctuations are expected to appear in the matter produced in relativistic heavy-ion collisions if it undergoes a first-order phase transition from the quark-gluon plasma to the hadronic matter. In the case that the density fluctuations can survive final-state interactions during the hadronic evolution and persist until the kinetic freeze-out, they then provide a unique probe to the critical endpoint (CEP), at which the first-order phase transition changes to a smooth crossover, in the QCD phase diagram. In the present study, we demonstrate for the first time that information on the neutron relative density fluctuation at freeze-out can be obtained from the yield ratio of light nuclei in heavy-ion collisions. From recent results on the p, d and 3H yields in central Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS) energies measured by the NA49 Collaboration, we observe a non-monotonic behavior of ∆n as a function of the collision energy with a peak at \sqrt{s_{NN}} = 8.8 GeV, suggesting that the QGP produced at this collision energy may have passed through the CEP during its evolution.
https://arxiv.org/pdf/1702.07620.pdf