  A major goal of the hot QCD program, the extraction of the properties of the
quark gluon plasma (QGP), is currently limited by our poor knowledge of the
initial condition of the QGP, in particular how it is shaped from the colliding
nuclei. To attack this limitation, we propose to exploit collisions of selected
species to precisely assess how the initial condition changes under variations
of the structure of the colliding ions. This knowledge, combined with
event-by-event measures of particle correlations in the final state of
heavy-ion collisions, will provide in turn a new way to probe the collective
structure of nuclei, and to confront and exploit the predictions of
state-of-the-art ab initio nuclear structure theories. The US nuclear community
should capitalize on this interdisciplinary connection by pursuing collisions
of well-motivated species at high-energy colliders.
