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Introduction to the PHENIX Experiment
 At very high temperatures, the vacuum is
not just "empty space" devoid of matter but is actually filled with virtual
quarks and gluons, the ultimate building blocks of matter. For example, at T
~150 MeV - more than 10 000 times hotter than the interior of the sun - our
normal hadronic world that has quarks and gluons confined inside protons and
neutrons is expected to "melt" into a phase of free quarks and gluons, the
so-called "quark gluon plasma."
In the early
Universe, about 1-10 usec after the big bang, the reverse process has led to the
formation of hadrons. At the Relativistic
Heavy Ion Collider (RHIC) at Brookhaven
National Laboratory (BNL) we study the properties of the vacuum at high
energy densities by colliding heavy nuclei, such as gold, and then
reconstructing the collision products. In an exciting link, it appears that our
understanding of proton sub-structure is closely connected to the physics of the
quantum chromodynamics (QCD) vacuum at high energy densities: the properties of
the proton cannot be understood without taking into account the complex "sea" of
virtual quark, anti-quark pairs and gluons inside the proton. At RHIC, we study the sub-structure of protons
in proton-nucleus and polarized proton-proton collisions leading to a very broad
and rigorous program in the physics of hadrons and QCD as the theory describing
their interactions and structure.
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