\frac{1}{2\pi}(1 &+& 2 v_1(y,p_T,N_p,h) 
\cos\phi  \nonumber
\\   &+&  2 v_2(y,p_T,N_p,h) \cos 2 \phi + \cdots ) \;\;.
\label{floweq}\end{aligned}$$ The “radial flow” component, “1” , is identified [@Cheng:2003as] from the hadron mass dependence of the blue shifted transverse momentum spectra $$\frac{dN_h(N_p)}{dydp_T^2}\sim \exp[ -m_h\cosh(\rho_\perp-\beta(y))/T_f] \;\;,$$ where $m_h(\sinh(\rho_\perp),\cosh(\rho_\perp))=(p_\perp,\sqrt{m_h^2+p_\perp^2})$ and $\beta(y)$ is the mean collective transverse flow rapidity at $y$.

![First line of evidence: Bulk collective flow is the barometric signature of QGP production. Left figure combines STAR  and PHENIX  measurements of the azimuthal elliptic flow ($v_2(p_T)$) of $\pi,K,p,\Lambda$ in Au+Au at 200 AGeV. The predicted hydrodynamic flow pattern from agrees well with observations in the bulk $p_T<1$ GeV domain. Right figure from shows $v_2$ scaled to the initial elliptic spatial anisotropy, $\epsilon$, as a function of the charge particle density per unit transverse area. The bulk hydrodynamic limit is only attained at RHIC.[]{data-label="line1fig"}](Line1fig.eps "fig:"){height="0.35\textheight" width="47.00000%"} ![First line of evidence: Bulk collective flow is the barometric signature of QGP production. Left figure combines STAR  and PHENIX  measurements of the azimuthal elliptic flow ($v_2(p_T)$) of $\pi,K,p,\Lambda$ in Au+Au at 200 AGeV. The predicted hydrodynamic flow pattern from agrees well with observations in the bulk $p_T<1$ GeV domain. Right figure from shows $v_2$ scaled to the 