  The PHENIX collaboration presents a concept for a major upgrade to the PHENIX
detector at the Relativistic Heavy Ion Collider (RHIC). This upgrade, referred
to as sPHENIX, brings exciting new capability to the RHIC program by opening
new and important channels for experimental investigation and utilizing fully
the luminosity of the recently upgraded RHIC facility. sPHENIX enables a
compelling jet physics program that will address fundamental questions about
the nature of the strongly coupled quark-gluon plasma discovered experimentally
at RHIC to be a perfect fluid. The upgrade concept addresses specific questions
whose answers are necessary to advance our understanding of the quark-gluon
plasma: (1) How to reconcile the observed strongly coupled quark-gluon plasma
with the asymptotically free theory of quarks and gluons? (2) What are the
dynamical changes to the quark-gluon plasma in terms of quasiparticles and
excitations as a function of temperature? (3) How sharp is the transition of
the quark-gluon plasma from the most strongly coupled regime near Tc to a
weakly coupled system of partons known to emerge at asymptotically high
temperatures? In three Appendices, we detail the additional physics
capabilities gained through further upgrades: (A) two midrapidity detector
additions, (B) a forward rapidity upgrade, and (C) an evolution to an ePHENIX
detector suitable for a future Electron Ion Collider at RHIC.
