\bf dA}$, is critical at any energy because the QCD plasma must first be created from pure kinetic energy! There has been no hot QGP in the universe (except in cosmic ray collisions) since the last drop condensed into hadrons about 13 billion years ago. Cold crystalline quark matter may lurk in the cores of neutron stars, but the transient hot QGP must be “materialized” in the lab. The “matter” arises from decoherence of [*virtual*]{} quantum chromo fluctuations in the initial wavefuntions of high energy nuclei.

At ultra-relativistic energies, these virtual fluctuations are frozen out due to time dilation into what has been called a Color Glass Condensate (CGC) [@McLerran:2004fg]. The CGC is the high density generalization of the Bjorken-Feynman dilute parton model. At high field strengths, the non-linear interactions of virtual quantum color fluctuations are predicted to limit the very small Bjorken $x_{BJ}\rightarrow 0$ Fourier components. The saturation property of CGC is related to unitarity constraints and determines the maximal entropy that can be produced in $AA$ at a given $\sqrt{s}$ as also pointed out by EKRT [@Eskola:2002qz].

The ${\rm \bf dA}$ control is needed to characterize to what extent these nonlinear initial state physics effects can be differentiated 