Momentum dissipation and evolution of the bulk-medium produced in Au-Au collisions at RHIC

A summary of two-particle number and transverse momentum ($p_t$) correlation results is presented which provides evidence for and properties of the highly dissipative medium formed in RHIC collisions. Large momentum scale two-particle correlation measurements in Au-Au collisions at $\sqrt{s_{NN}}$ = 130 GeV [1] have now been extended to 62 and 200 GeV, and to finer centrality bins. Number correlations on transverse momentum coordinates reveal strong momentum dissipation of low-$Q^2$ partons to the soft, bulk medium causing increased fluctuations. Similar correlation studies on pseudorapidity ($\eta$) and azimuth ($\phi$) indicate dramatic evolution of the same-side, low-$Q^2$ parton correlation peak with centrality. Net-charge correlations reveal a qualitative change of hadronization geometry from one-dimensional longitudinal fragmentation in p-p to two-dimensional bulk fragmentation in central Au-Au. Other features of the net-charge correlation data imply the development of an opaque medium. Transverse momentum correlations on $\eta,\phi$ suggest that the bulk medium recoils collectively in response to parton stopping. Current results will be shown and the data compared to Hijing and other model predictions. [1] J. Adams et al., Phys. Lett. B634, 347 (2006); nucl-ex/0411003; nucl-ex/0408012.