The "soft ridge" -- is it initial-state geometry or modified jets?

An $\eta$-elongated same-side 2D peak ("soft ridge") in minimum-bias angular correlations from heavy ion collisions has been attributed both to jet formation and to initial-state geometry structure coupled to radial flow. We consider evidence for both interpretations.Comment: 4 pages, 3 figures, to be published in the Proceedings of the XLI International Symposium on Multiparticle Dynamics (ISMD 2011), 26-30 September, 2011, Miyajima Island, Hiroshima, Japa

Collectivity and manifestations of minimum-bias jets in high-energy nuclear collisions

Collectivity, as interpreted to mean flow of a dense medium in high-energy A-A collisions described by hydrodynamics, has been attributed to smaller collision systems -- p-A and even p-p collisions -- based on recent analysis of LHC data. However, alternative methods reveal that some data features attributed to flows are actually manifestations of minimum-bias (MB) jets. In this presentation I review the differential structure of single-particle $p_t$ spectra from SPS to LHC energies in the context of a two-component (soft + hard) model (TCM) of hadron production. I relate the spectrum hard component to measured properties of isolated jets. I use the spectrum TCM to predict accurately the systematics of ensemble-mean $\bar p_t$ in p-p, p-A and A-A collision systems over a large energy interval. Detailed comparisons of the TCM with spectrum and correlation data suggest that MB jets play a dominant role in hadron production near midrapidity. Claimed flow phenomena are better explained as jet manifestations agreeing quantitatively with measured jet properties.Comment: 10 pages, 8 figures, Proceedings of XLVII International Symposium on Multiparticle Dynamics, Tlaxcala City, Mexico, September 11-15, 201

Low-Q2Q^2 partons in p-p and Au-Au collisions

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 $$ 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.Comment: 6 pages, 4 figures, XXXV International Symposium on Multiparticle Dynamics 2005, Krom\^{e}\^{r}\'{i}\^{z}, Czech Republic, August 9-15, 200