Transits of the QCD Critical Point

Abstract

We analyze the evolution of hydrodynamic fluctuations in a heavy ion collision as the system passes close to the QCD critical point. We introduce two small dimensionless parameters $\lambda$ and ${\Delta }_s$ to characterize the evolution. $\lambda$ compares the microscopic relaxation time (away from the critical point) to the expansion rate $\lambda \equiv {\tau }_0/{\tau }_Q$, and ${\Delta }_s$ compares the baryon to entropy ratio, $n/s$, to its critical value, ${\Delta }_s\equiv (n/s-n_c/s_c)/(n_c/s_c)$. We determine how the evolution of critical hydrodynamic fluctuations depends parametrically on $\lambda$ and ${\Delta }_s$. Finally, we use this parametric reasoning to estimate the critical fluctuations and correlation length for a heavy ion collision, and to give guidance to the experimental search for the QCD critical point.

Comments: 42 pages, 5 figures