of the pressure, $P(T)/T^4$, and a measure of the deviation from the ideal Stefan-Boltzmann limit $(\epsilon(T)-3 P(T))/T^4$. Note that the scale on both graphs has not been corrected for finite lattice volume effects: see for discussion. []{data-label="qgpfig1"}](FodorKatz_P_e_mu0.eps){height="0.35\textheight" width="100.00000%"}

![Important features of the QGP equation of state. The speed of sound $c_s^2=d\epsilon/dP$ drops below $1/3$ for $T<2T_c \approx300$ MeV. Right panel shows a current estimate of the location of the tricritical point at finite baryon density []{data-label="qgpfig2"}](SoundSpeed_Fig2b.eps "fig:"){height="0.35\textheight" width="45.00000%"} ![Important features of the QGP equation of state. The speed of sound $c_s^2=d\epsilon/dP$ drops below $1/3$ for $T<2T_c \approx300$ MeV. Right panel shows a current estimate of the location of the tricritical point at finite baryon density []{data-label="qgpfig2"}](FodorKatz_Tmu.eps "fig:"){height="0.45\textheight" width="45.00000%"}

Another distinctive feature of the QGP phase diagram is shown in the right panel in Fig.(\[qgpfig2\]). Recent lattice QCD calculations [@Fodor:2004nz] have begun to converge on numerical evidence that the QGP may have a second tricritical point [@Halasz:1998qr; @Rischke:2003mt] at moderate baryon densities with $\mu_B=3\mu_q\sim 360$ MeV and $T\sim T_c$.

QCD predictions of the QGP phase date back thirty years [@Collins:1974ky] and followed immediately after the discovery of asymptotic freedom of QCD. The experimental strategies to search for new forms of dense 