System size and beam energy dependence of azimuthal anisotropy from PHENIX

We present azimuthal anisotropy measurements in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV. Comparison between reaction plane and cumulant $v_2$ measurements in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV show that non-flow contributions, originating mainly from jets, influence the extracted $v_2$ for $p_T$ $\gtrsim$ 3.5 GeV/c. Number of constituent quark (NCQ) scaling of $v_2$, when studied as a function of transverse kinetic energy $KE_T$, is seen to hold for Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV and for Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV for $KE_{T}$ $\lesssim$ 1 GeV/c. Differential hexadecupole flow $v_4$ seems to exhibit scaling with integral $v_2$ for centrality $\le$ 40% as has been observed for differential $v_2$.Comment: 4 pages, 3 figures, Proceedings of the QM2008 Conference, Jaipur, India February 4-10 200

Universal scaling of the elliptic flow data at RHIC

Recent PHOBOS measurements of the excitation function for the pseudo-rapidity dependence of elliptic flow in Au+Au collisions at RHIC, have posed a significant theoretical challenge. Here we show that these differential measurements, as well as the RHIC measurements on transverse momentum satisfy a universal scaling relation predicted by the Buda-Lund model, based on exact solutions of perfect fluid hydrodynamics. We also show that recently found transverse kinetic energy scaling of the elliptic flow is a special case of this universal scaling.Comment: 4 pages, 3 figures, 1 tabl

Has the QCD Critical Point been Signaled by Observations at RHIC ?

The shear viscosity to entropy ratio ($\eta/s$) is estimated for the hot and dense QCD matter created in Au+Au collisions at RHIC ($\sqrt{s_{NN}}=200$ GeV). A very low value is found $\eta/s \sim 0.1$, which is close to the conjectured lower bound ($1/4\pi$). It is argued that such a low value is indicative of thermodynamic trajectories for the decaying matter which lie close to the QCD critical end point.Comment: 4 pages, 3 figures. Revised version, accepted for publication in PR

Optimum temperature and stocking density for transportation of tilapia (Oreochromis niloticus) broodstock in the semi-arid zone of Nigeria

Oreochromis niloticus broodstock of mean weight 32.3g were cropped in the morning with dragnet from a 1 ha reservoir and transported in round tanks to the Hatchery complex of the National Institute for Freshwater Fisheries Research where they were stocked into 5m x 5m indoor concrete tanks filled with clean water and with aerators at a density of 4 fish/m1. They were acclimated for 5 days and then packaged into 60 liter capacity water proof bags at the following stocking densities: 60, 80, 100, 120, 140 fish/60 lit bag. Each stocking density had bags with ice blocks and bags without ice blocks in triplicate. The water proof bags were oxygenated, loaded into quick fitting plastic bowls and transported in a bus from New Bussa to Warra, Kebbi state, a journey of 3 hours. The trip was repeated four times. Percentage survival in bags with ice block were 100%for stocking densities 60, 80, 100 fish/60 lit bag, 95.1%for 120 fish/60 lit bag and 84. 7%for 1-10 fish/60 lit bag (mean temperature 23.5~?C). Mortalities were recorded in all the bags without ice block but the highest survival was in the bag with stocking density 60fish/60 lit bag (mean temperature 29.2~?C)

Decomposition of Harmonic and Jet Contributions to Particle-pair Correlations at Ultra-relativistic Energies

Methodology is presented for analysis of two-particle azimuthal angle correlation functions obtained in collisions at ultra-relativistic energies. We show that harmonic and di-jet contributions to these correlation functions can be reliably decomposed by two techniques to give an accurate measurement of the jet-pair distribution. Results from detailed Monte Carlo simulations are used to demonstrate the efficacy of these techniques in the study of possible modifications to jet topologies in heavy ion reactions.Comment: Updated version to be published in PRC Rapid Com

Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX

The intermediate $p_T$ region (2 - 5 GeV/$c$) in central Au+Au collisions at RHIC has a rich physics content. The (anti)proton to pion ratio at the intermediate $p_T$ gives us a powerful tool to investigate the bulk properties of the hot and dense matter created at RHIC and their hadronization processes. We present the preliminary results of identified charged hadron spectra at the lower beam energies at RHIC. The excitation function of (anti)proton to pion ratios from SPS to RHIC are shown. We also discuss the onset of the baryon enhancement at the high energy heavy ion collisions.Comment: 4 pages, 3 figures, Quark Matter 2006 conference proceeding

Multiparticle angular correlations: a probe for the sQGP at RHIC

A novel decomposition technique is used to extract the centrality dependence of di-jet properties and yields from azimuthal correlation functions obtained in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$=200 GeV. The width of the near-side jet shows very little dependence on centrality. In contrast, the away-side jet indicates substantial broadening as well as hints for for a local minimum at $\Delta \phi=\pi$ for central and mid-central events. The yield of jet-pairs (per trigger particle) slowly increases with centrality for both the near- and away-side jets. These observed features are compatible with several recent theoretical predictions of possible modifications of di-jet fragmentation by a strongly interacting medium. Several new experimental approaches, including the study of flavor permutation and higher order multi-particle correlations, that might help to distinguish between different theoretical scenarios are discussed.Comment: Proceedings of the MIT workshop on correlations and fluctation

Near-threshold production of the multi-strange Ξ−\Xi^- hyperon

The yield for the multi-strange $\Xi^{-}$ hyperon has been measured in 6 AGeV Au+Au collisions via reconstruction of its decay products $\pi^{-}$ and $\Lambda$, the latter also being reconstructed from its daughter tracks of $\pi^{-}$ and p. The measurement is rather close to the threshold for $\Xi^{-}$ production and therefore provides an important test of model predictions. The measured yield for $\Xi^{-}$ and $\Lambda$ are compared for several centralities. In central collisions the $\Xi^{-}$ yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multi-strange hadron production approaches chemical equilibrium in high baryon density nuclear matter.Comment: Submitted to PR

Quark-Gluon Matter

A concise review of the experimental and phenomenological progress in high-energy heavy-ion physics over the past few years is presented. Emphasis is put on measurements at BNL-RHIC and CERN-SPS which provide information on fundamental properties of QCD matter at extreme values of temperature, density and low-x. The new opportunities accessible at the LHC, which may help clarify some of the current open issues, are also outlined.Comment: Minor changes to text. New refs. included. Updated figures with final dat

Medium modification of jet fragmentation in Au+Au collisions at sqrt(s_NN)=200 GeV measured in direct photon-hadron correlations

The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the photon is an excellent approximation to the initial p_T of the jet and the ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_ AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z_T. The fragment yield at low z_T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.Comment: 562 authors, 70 insitutions, 8 pages, and 3 figures. Submitted to Phys. Rev. Lett. v2 has minor changes to improve clarity. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm