After 15 years of successful data taking the PHENIX experiment at the Relativistic Heavy Ion
Collider, RHIC, at Brookhaven National Laboratory, BNL, is undergoing a major update to ex-
pand its physics capabilities. The originally four experiments were designed to study high energy
heavy ion collisions to create a dense, high temperature matter called the Quark Gluon Plasma,
QGP . This QGP is believed to be a stage of the forming universe a few microseconds af-
ter the big bang. RHIC showed that in high energy collisions of gold nuclei one performs that
phase transition from nuclear matter to the QGP. Its temperature was measured to over 4 trillion
degrees and studies of the density showed that the QGP behaves like a perfect liquid with hardly
any viscosity. The best tool to study the properties of the QGP turns out to be jets from hard
quark–quark or quark–photon scattering as data from RHIC and the Large Hadron Collider, LHC
, have shown. A necessity for a detailed jet measurement is hermetic calorimeter coverage
which none of the RHIC experiment currently has. Also the melting of quark bound states like
the $\jmath$ = $\psi$ and $\gamma$ states in the QGP are one of the proposed measurements. This let to a redesign of the
PHENIX experiment into an updated version currently called sPHENIX to address these challenges.
Recently sPHENIX was granted CD-0 from DOE, with a planned installation by 2021 and first
measurements in 2022.