Slowing Out of Equilibrium Near the QCD Critical Point

Abstract

The QCD phase diagram may feature a critical end point at a temperature T and baryon chemical potential $μ$ which is accessible in heavy ion collisions. The universal long wavelength fluctuations which develop near this Ising critical point result in experimental signatures which can be used to find the critical point. The magnitude of the observed effects depends on how large the correlation length $ξ$ becomes. Because the matter created in a heavy ion collision cools through the critical region of the phase diagram in a finite time, critical slowing down limits the growth of $ξ$, preventing it from staying in equilibrium. This is the fundamental nonequilibrium effect which must be calculated in order to make quantitative predictions for experiment. We use universal nonequilibrium dynamics and phenomenologically motivated values for the necessary nonuniversal quantities to estimate how much the growth of $ξ$ is slowed.