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abstract: 'Three empirical lines of evidence, $({\rm \bf P_{QCD}, pQCD, dA)}$, from RHIC have converged and point to the discovery of a strongly coupled Quark Gluon Plasma. The evidence includes (1) bulk collective elliptic flow and (2) jet quenching and mono-jet production, observed in Au+Au collisions at 200 AGeV, and (3) a critical control experiment using D+Au at 200 AGeV.'
author:
- 'M. Gyulassy'
---

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The Theoretical QGP
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The Standard Model of strong interactions predicts the existence of a new phase of matter, called a Quark Gluon Plasma (QGP), in which the quark and gluon degrees of freedom normally confined within hadrons are mostly liberated. Lattice QCD calculations show that there is a rapid rise of the entropy density, $\sigma(T)$, of matter when the temperature reaches $T\approx T_c\sim 160$ MeV. Beyond $T_c$ the effective number of degrees of freedom, $n(T)$, saturates near the number of quark and gluon helicity states $n_{QCD}=8_c\times 2_s + \frac{7}{8}\times 3_c\times N_f\times 2_s\times 2_{q\bar{q}}\approx
37$. The entropy density $\sigma(T)=dP/dT=(\epsilon+P)/T\propto n(T)T^3$ approaches the Stefan Boltzmann limit $4P_{SB}(T)/3T$. The transition region is a smooth crossover when dynamical quarks are taken into account, but the width of the transition region remains relatively narrow, $\Delta T_c/T_c \sim 