Critical phenomena in deep inelastic scattering

Saturation in deep inelastic scattering (DIS) and deeply virtual Compton scattering is associated with a phase transition between the partonic gas, typical of moderate $x$ and $Q^2$, and a partonic fluid (liquid), appearing at increasing $Q^2$ and decreasing Bjorken $x$. In the statistical interpretation of DIS, the large-$x$, $(1-x)^n$ factor in the structure functions is associated with a statistical distribution (perfect gas), while the low-$x$, Regge behaved factor $x^{b(Q^2)}$ introduces deviation from the perfect gas and ultimately leads to a gas-liquid phase transition.