"Figure 4a" of "Measurement of density correlations in pseudorapidity via charged particle multiplicity fluctuations in Au+Au collisions at sqrt(s_NN)=200 GeV"

Longitudinal density correlations of produced matter in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV have been measured from the inclusive charged particle distributions as a function of pseudorapidity window sizes. The extracted $\alpha\xi$ parameter, related to the susceptibility of the density fluctuations in the long wavelength limit, exhibits a non-monotonic behavior as a function of the number of participant nucleons, $N_{part}$. A local maximum is seen at $N_{part}$ ~ 90, with corresponding energy density based on the Bjorken picture of $\epsilon_{B_j}\tau$ ~ 2.4 GeV/($fm^2$ $c$) with a transverse area size of 60 $fm^2$. This behavior may suggest a critical phase boundary based on the Ginzburg-Landau framework.