Low-$Q^2$ partons in p-p and Au-Au collisions

Abstract

We describe correlations of low-$Q^2$ parton fragments on transverse rapidity $y_t$ and angles $(\eta,\phi)$ from p-p and Au-Au collisions at $\sqrt{s} =$ 130 and 200 GeV. Evolution of correlations on $y_t$ from p-p to more-central Au-Au collisions shows evidence for parton dissipation. Cuts on $y_t$ isolate angular correlations on $(\eta,\phi)$ for low-$Q^2$ partons which reveal a large asymmetry about the jet thrust axis in p-p collisions favoring the azimuth direction. Evolution of angular correlations with increasing Au-Au centrality reveals a rotation of the asymmetry to favor pseudorapidity. Angular correlations of transverse momentum $p_t$ in Au-Au collisions access temperature/velocity structure resulting from low-$Q^2$ parton scattering. $p_t$ autocorrelations on $(\eta,\phi)$, obtained from the scale dependence of $<p_t>$ fluctuations, reveal a complex parton dissipation process in heavy ion collisions which includes the possibility of collective bulk-medium recoil in response to parton stopping.