Relativistic heavy-ion collisions are used in particle and high energy physics to study theconditions of the early universe in the laboratory by heating nuclear matter to tempera-tures above the quark-gluon de-confinement temperature. Just a few microseconds afterthe Big Bang, the universe was partially filled with a thermally equilibrated system calledquark-gluon plasma (QGP). As the QGP cooled, the free quarks and gluons combined intoparticles like protons and neutrons which bounded together below the critical temperatureto form light nuclei. The Relativistic Heavy-Ion Collider (RHIC) at Brook-haven NationalLaboratory (BNL) create the condition similar to the early universe to understand whathappens to ordinary nuclear matter at high temperatures and higher densities by the ther-modynamic properties and transport coefficients of the medium. The transport coefficientssuch as shear and bulk viscosity, conductivity, diffusivity, etc. are studied to learn about theinteractions which in equilibrium are characterized by a temperature T and baryon chemicalpotentialμB. The strongly QGP was first discovered at RHIC in 2005 and was found to actlike an almost “perfect” liquid, because it has a low viscosity to entropy ratio. The primarytheoretical tool used to study QGP is lattice QCD, which allows first principle calculations.
Celestine SegbefiaBall State University – Department of Physics and Astronomy