  In this document the PHENIX collaboration proposes a major upgrade to the
PHENIX detector at the Relativistic Heavy Ion Collider. This upgrade, sPHENIX,
enables an extremely rich jet and beauty quarkonia physics program addressing
fundamental questions about the nature of the strongly coupled quark-gluon
plasma (QGP), discovered experimentally at RHIC to be a perfect fluid. The
startling dynamics of the QGP on fluid-like length scales is an emergent
property of quantum chromodynamics (QCD), seemingly implicit in the Lagrangian
but stubbornly hidden from view. QCD is an asymptotically free theory, but how
QCD manifests as a strongly coupled fluid with specific shear viscosity near
$T_C$, as low as allowed by the uncertainty principle, is as fundamental an
issue as that of how confinement itself arises.
