Soft Contribution to the Hard Ridge in Relativistic Nuclear Collisions

Nuclear collisions exhibit long-range rapidity correlations not present in proton-proton collisions. Because the correlation structure is wide in relative pseudorapidity and narrow in relative azimuthal angle, it is known as the ridge. Similar ridge structures are observed in correlations of particles associated with a jet trigger (the hard ridge) as well as correlations without a trigger (the soft ridge). Earlier we argued that the soft ridge arises when particles formed in an early Glasma stage later manifest transverse flow. We extend this study to address new soft ridge measurements. We then determine the contribution of flow to the hard ridge.Comment: 16 pages, 9 figures, includes comparison to dat

Estimation of shear viscosity based on transverse momentum correlations

Event anisotropy measurements at RHIC suggest the strongly interacting matter created in heavy ion collisions flows with very little shear viscosity. Precise determination of "shear viscosity-to-entropy" ratio is currently a subject of extensive study. We present preliminary results of measurements of the evolution of transverse momentum correlation function with collision centrality of $Au +Au$ interactions at $\sqrt{s_{NN}}$ = 200 GeV. We compare two differential correlation functions, namely {\it inclusive} and a differential version of the correlation measure $\tilde C$ introduced by Gavin ${\it et. al.}$. These observables can be used for the experimental study of the shear viscosity per unit entropy.Comment: 4 pages, 8 figures, proceedings re-submitted for Quark Matter 2009 conference. This paper contains revision of one of the figure

The Rise and Fall of the Ridge

Recent data from heavy ion collisions at RHIC show unexpectedly large near-angle correlations that broaden longitudinally with centrality. The amplitude of this ridge-like correlation rises rapidly with centrality, reaches a maximum, and then falls in the most central collisions. In this talk we explain how this behavior can be easily understood in a picture where final momentum-space correlations are driven by initial coordinate space density fluctuations. We propose $v_n^2/\epsilon_{n,part}^{2}$ as a useful way to study these effects and explain what it tells us about the collision dynamics.Comment: 6 pages, 5 figures, proceedings for Hard Probes 2010 in Eilat, Israe

Transverse Radial Flow Effects on Two- and Three-Particle Angular Correlations

We use a simple a transverse radial boost scenario coupled to PYTHIA events to illustrate the impact radial flow may have on two- and three-particle correlation functions measured in heavy-ion collisions. We show that modest radial velocities can impart strong modifications to the correlation functions, some of which may be interpreted as same side ridge and away side structure that can mimic conical emission.Comment: 7 figures, 9 pages, Material presented in part by Pruneau at HOC 07, Montreal, Canada Accepted for publication in Nucl Phys A (Jan 2008

OPEN CHARM PRODUCTION IN HADRONIC AND HEAVY-ION COLLISIONS AT RHIC AND LHC ENERGIES TO O(αs3)O(\alpha_s^3)

We present results on rapidity and transverse momentum distributions of inclusive charm quark production in hadronic and heavy-ion collisions at RHIC and LHC energies, including the next-to-leading order, $O(\alpha_s^3)$, radiative corrections and the nuclear shadowing effect. We determine the hadronic and the {\it effective} (in-medium) K-factor for the differential and total inclusive charm cross sections. We show that these K-factors have strong $p_T$ dependence. We discuss how measurements of charm production at RHIC and LHC can provide valuable information about the gluon density in a nucleus.Comment: LaTex, 4 pages, 2 figs (available on request) Talk presented at Eleventh International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions -- Quark Matter '95, Monterey, CA, January 9-13, 1995

Traces of Thermalization at RHIC

I argue that measurements of Au+Au collisions at 20, 130 and 200 GeV of the centrality dependence of the mean p_t together with p_t and net-charge fluctuations reflect the approach to local thermal equilibrium.Comment: 4 pages, 4 eps figures, for proc. Quark Matter 2004, to be published in J. Phys.

Heavy Ion Physics at the LHC

The ion-ion center of mass energies at the LHC will exceed that at RHIC by nearly a factor of 30, providing exciting opportunities for addressing unique physics issues in a completely new energy domain. Some highlights of this new physics domain are presented here. We briefly describe how these collisions will provide new insights into the high density, low momentum gluon content of the nucleus expected to dominate the dynamics of the early state of the system. We then discuss how the dense initial state of the nucleus affects the lifetime and temperature of the produced system. Finally, we explain how the high energy domain of the LHC allows abundant production of `rare' processes, hard probes calculable in perturbative quantum chromodynamics, QCD. At the LHC, high momentum jets and $b \bar b$ bound states, the $\Upsilon$ family, will be produced with high statistics for the first time in heavy ion collisions.Comment: 10 pages, 2 figures, proceedings of INPC 04 in Goteborg, Sweden, July 2004, includes conference style fil

Highlights from STAR: probing the early medium in heavy ion collisions

We present highlights of recent results from the STAR Collaboration at RHIC, focusing on the properties of the early medium created in heavy ion collisions. We emphasize the strangeness production including the observation of a hypernucleus (the hypertriton), the observation of reaction-plane-dependent angular correlation of charged particles searching for local strong parity violation effects in heavy ion collisions, and the evaluation of the medium viscosity from measurements of elliptic flow. We discuss STAR's plan for the "Critical Point Search" program at RHIC.Comment: 8 pages, 10 figures, proceedings of the QM2009 talk Minor changes in the texts and format have been done for publicatio

Quarkonium production via recombination

The contrast between model predictions for the transverse momentum spectra of J/Psi observed in Au-Au collisions at RHIC is extended to include effects of nuclear absorption. We find that the difference between initial production and recombination is enhanced in the most central collisions. Models utilizing a combination of these sources may eventually be able to place constraints on their relative magnitudes.Comment: Based on invited plenary talk at the 2nd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, Asilomar, CA, June 9-16, 2006, to be published in Nucl. Phys.

Viscosity and the Soft Ridge at RHIC

Correlation studies exhibit a ridge-like feature in rapidity and azimuthal angle, with and without a jet trigger. We ask whether the feature in untriggered correlations can be a consequence of transverse flow and viscous diffusion.Comment: Proc. Quark Matter 2008, Jaipur, Indi