The strongly coupled quark-gluon plasma created at RHIC

Abstract

The Relativistic Heavy Ion Collider (RHIC) was built to re-create and study in the laboratory the extremely hot and dense matter that filled our entire universe during its first few microseconds. Its operation since June 2000 has been extremely successful, and the four large RHIC experiments have produced an impressive body of data which indeed provide compelling evidence for the formation of thermally equilibrated matter at unprecedented temperatures and energy densities -- a "quark-gluon plasma (QGP)". A surprise has been the discovery that this plasma behaves like an almost perfect fluid, with extremely low viscosity. Theorists had expected a weakly interacting gas of quarks and gluons, but instead we seem to have created a strongly coupled plasma liquid. The experimental evidence strongly relies on a feature called "elliptic flow" in off-central collisions, with additional support from other observations. This article explains how we probe the strongly coupled QGP, describes the ideas and measurements which led to the conclusion that the QGP is an almost perfect liquid, and shows how they tie relativistic heavy-ion physics into other burgeoning fields of modern physics, such as strongly coupled Coulomb plasmas, ultracold systems of trapped atoms, and superstring theory.

10 pages, 1 figure. Writeup of an invited talk given at the International Conference on Strongly Coupled Coulomb Systems 2008 (SCCS 2008), 29 July - 2 August 2008, Camerino, Italy. To appear in the proceedings, published in a special issue of Journal of Physics A

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• Improved thermodynamics of SU(2) gauge theory
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• System size dependence of the hadronic rescattering effect at energies available at the CERN Large Hadron Collider
• Hydrodynamic description of $D$ meson production in high-energy heavy-ion collisions
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• Toward parton equilibration with improved parton interaction matrix elements
• Measurement of f${}_1$(1285) production in pp collisions at $\sqrt{\text{s}}$ = 13 TeV
• Probing the Chiral Magnetic Wave with charge-dependent flow measurements in Pb-Pb collisions at the LHC
• Perspectives in Small Systems : Heavy Quarks and HBT Radii
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• Effect of $\alpha$-clusters on particle production in O$-$O and p$-$O collisions at LHC energies
• Probing Quarkonium Diffusion in a Magnetized Quark-Gluon Plasma
• London model of dual color superconductor
• Implications of correlations and fluctuations in small systems