We study the time evolution of conserved-charge fluctuations near the QCD critical point and show how the existence of the critical point is observed in experimental measurements of fluctuation observables in heavy ion collisions.
The soft mode of the QCD critical point should obey a diffusion equation because it is a linear combination of the chiral condensate and conserved densities, i.e., baryon number density and energy density. The baryon fluctuation can represent the critical dynamics, while the chiral fluctuation mode is a slave mode of the conserved densities.
We propose a stochastic diffusion equation in the rapidity space with critical nature being encoded in the time-dependent diffusion coefficient and baryon number susceptibility. We find a novel non-monotonic dependence of the critical fluctuation observables on the rapidity cuts, depending on the approach to the critical point during the time evolution. We show that the effect of critical dynamics could be sustainable as a non-monotonic behavior as the rapidity-window dependence of conserved-charge cumulants at the kinetic freeze-out. We emphasize this rapidity-window dependence as a unique and robust signal for the critical point search in experiments.
|Preferred Track||Correlations and Fluctuations|