Meson and baryon elliptic flow at high pT from parton coalescence

The large and saturating differential elliptic flow v2(pT) observed in Au+Au reactions at RHIC so far could only be explained assuming an order of magnitude denser initial parton system than estimated from perturbative QCD. Hadronization via parton coalescence can resolve this ``opacity puzzle'' because it enhances hadron elliptic flow at large pT relative to that of partons at the same transverse momentum. An experimentally testable consequence of the coalescence scenario is that v2(pT) saturates at about 50% higher values for baryons than for mesons. In addition, if strange quarks have weaker flow than light quarks, hadron v2 at high pT decreases with relative strangeness content.Comment: Talk at SQM2003 [7th Int. Conf. on Strangeness in Quark Matter (Atlantic Beach, NC, USA, Mar 12-17, 2003)] - 6 pages, 5 eps figs, IOP style file

Particle dependence of elliptic flow in Au+Au collisions at sNN=\sqrt{s_{NN}}= 200 GeV

The elliptic flow parameter ($v_2$) for $K_S^0$ and $\Lambda+\bar{\Lambda}$ has been measured at mid-rapidity in Au + Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV by the STAR collaboration. The $v_2$ values for both $K_S^{0}$ and $\Lambda+\bar{\Lambda}$ saturate at moderate $p_T$, deviating from the hydrodynamic behavior observed in the lower $p_T$ region. The saturated $v_2$ values and the $p_T$ scales where the deviation begins are particle dependent. The particle-type dependence of $v_2$ shows features expected from the hadronization of a partonic ellipsoid by coalescence of co-moving quarks. These results will be discussed in relation to the nuclear modification factor ($R_{CP}$) which has also been measured for $K_S^0$ and $\Lambda+\bar{\Lambda}$ by the STAR collaboration.Comment: 6 pages, 3 figures, Strange Quark Matter 2003 Conference (SQM 2003): updated with 2 figures from original talk that did not appear in the journa

Particle correlations at RHIC from parton coalescence dynamics -- first results

A new dynamical approach that combines covariant parton transport theory with hadronization channels via parton coalescence and fragmentation is applied to Au+Au at RHIC. Basic consequences of the simple coalescence formulas, such as elliptic flow scaling and enhanced proton/pion ratio, turn out to be rather sensitive to the spacetime aspects of coalescence dynamics.Comment: Contribution to Quark Matter 2004 (January 11-17, 2004, Oakland, CA). 4 pages, 2 EPS figs, IOP style fil

Systematic Errors in Sunyaev-Zeldovich Surveys of Galaxy Cluster Velocities

Galaxy cluster surveys compiled via the Sunyaev-Zeldovich Effect have the potential to place strong constraints on cosmology, and in particular the nature of dark energy. Here we consider cluster velocity surveys using kinetic Sunyaev-Zeldovich measurements. Cluster velocities closely trace the large-scale velocity field independent of cluster mass; we demonstrate that two useful cluster velocity statistics are nearly independent of cluster mass, in marked contrast to cluster number count statistics. On the other hand, cluster velocity determinations from three-band observations of Sunyaev-Zeldovich distortions can require additional cluster data or assumptions, and are complicated by microwave emission from dusty galaxies and radio sources, which may be correlated with clusters. Systematic errors in velocity due to these factors can give substantial biases in determination of dark energy parameters, although large cluster velocity surveys will contain enough information that the errors can be modeled using the data itself, with little degradation in cosmological constraints.Comment: 8 pages, 2 figures. Minor changes in the text to match the accepted version. Conclusions unchange

Suppression of High Transverse Momentum π0\pi^0 Spectra in Au+Au Collisions at RHIC

Au+Au, $s^{1/2} = 200$ A GeV measurements at RHIC, obtained with the PHENIX, STAR, PHOBOS and BRAHMS detectors, have all indicated a suppression of neutral pion production, relative to an appropriately normalized NN level. For central collisions and vanishing pseudo-rapidity these experiments exhibit suppression in charged meson production, especially at medium to large transverse momenta. In the PHENIX experiment similar behavior has been reported for $\pi^0$ spectra. In a recent work on the simpler D+Au interaction, to be considered perhaps as a tune-up for Au+Au, we reported on a pre-hadronic cascade mechanism which explains the mixed observation of moderately reduced $p_\perp$ suppression at higher pseudo-rapidity as well as the Cronin enhancement at mid-rapidity. Here we present the extension of this work to the more massive ion-ion collisions. Our major thesis is that much of the suppression is generated in a late stage cascade of colourless pre-hadrons produced after an initial short-lived coloured phase. We present a pQCD argument to justify this approach and to estimate the time duration $\tau_p$ of this initial phase. Of essential importance is the brevity in time of the coloured phase existence relative to that of the strongly interacting pre-hadron phase. The split into two phases is of course not sharp in time, but adequate for treating the suppression of moderate and high $p_\perp$ mesons.Comment: 19 pages, 10 figure

Recombination Models

We review the current status of recombination and coalescence models that have been successfully applied to describe hadronization in heavy ion collisions at RHIC energies. Basic concepts as well as actual implementations of the idea are discussed. We try to evaluate where we stand in our understanding at the moment and what remains to be done in the future.Comment: Plenary Talk at Quark Matter 2004, submitted to J. Phys. G, 8 pages, 3 figure

Hadronization in heavy ion collisions: recombination or fragmentation?

We show that hadron production in relativistic heavy ion collisions at transverse momenta larger than 2 GeV/c can be explained by the competition of two different hadronization mechanisms. Above 5 GeV/c hadron production can be described by fragmentation of partons that are created perturbatively. Below 5 GeV/c recombination of partons from the dense and hot fireball dominates. This can explain some of the surprising features of RHIC data like the constant baryon-to-meson ratio of about one and the small nuclear suppression for baryons between 2 to 4 GeV/c.Comment: Contribution to the 7th Conference on Strange Quark Matter (SQM 2003), submitted to J.Phys.G; 6 pages LaTeX, 4 eps figures, uses iopart.cl

Pion interferometry in Au+Au collisions at sNN\sqrt{\mathrm{s}_{_{\mathrm{NN}}}} = 200 GeV

We present a systematic analysis of two-pion interferometry in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector at RHIC. We extract the HBT radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianess of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast wave parameterizations. The expansion of the source and its relation with the initial energy density distribution is studied.Comment: 21 pages, 30 figures. As published in Physics Review

Pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV

We present a systematic analysis of two-pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV using the STAR detector at Relativistic Heavy Ion Collider. We extract the Hanbury-Brown and Twiss radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianness of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast-wave parametrizations. The expansion of the source and its relation with the initial energy density distribution is studied

Transverse-momentum dependent modification of dynamic texture in central Au+Au collisions at sqrt(S_NN)=200 GeV

Correlations in the hadron distributions produced in relativistic Au+Au collisions are studied in the discrete wavelet expansion method. The analysis is performed in the space of pseudorapidity (|eta| < 1) and azimuth (full 2 pi) in bins of transverse momentum (p_t) from 0.14 < p_t < 2.1 GeV/c. In peripheral Au+Au collisions a correlation structure ascribed to mini-jet fragmentation is observed. It evolves with collision centrality and p_t in a way not seen before which suggests strong dissipation of minijet fragmentation in the longitudinally-expanding medium.Comment: 6 pages, 3 figure, accepted as Phys.Rev.C Rapid Communication. This version fixes journal style issue