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

Reconstructed Jets at RHIC

To precisely measure jets over a large background such as pile up in high luminosity p+p collisions at LHC, a new generation of jet reconstruction algorithms is developed. These algorithms are also applicable to reconstruct jets in the heavy ion environment where large event multiplicities are produced. Energy loss in the medium created in heavy ion collisions are already observed indirectly via inclusive hadron distributions and di-hadron correlations. Jets can be used to study this energy loss in detail with reduced biases. We review the latest results on jet-medium interactions as seen in A+A collisions at RHIC, focusing on the recent progress on jet reconstruction in heavy ion collisions.Comment: Proceedings for the 26th Winter Workshop on Nuclear Dynamic

Recent Results on Strangeness Production at RHIC

Due to its large acceptance, the STAR experiment has acquired a wealth of data on strangeness production for a variety of collisions systems and energies, from p+p to Au+Au. By using the yields and spectra, we address the evolution of the bulk system, including strangeness enhancement and the flavour dependence of radial and elliptic flow. Utilising the fact that we can identify strange baryons and mesons, we investigate different hadronization mechanisms in the intermediate and high p$_{T}$ regions. The ratios of the particle yields, measured to high p$_{T}$, are used to further investigate the range and applicability of the previously reported anomalous baryon production. We also study two-particle azimuthal correlations of identified particles in order to investigate any flavour dependence of jet fragmentation in the available p$_{T}$ range. Data was presented for a number of different collision systems and energies.Comment: Proceedings of SQM'06 Conference, LA, 2006 (submitted to J. Phys. G

ϕ\phi meson production in sNN\sqrt{s_{NN}} = 200 GeV Au+Au and pp collisions at RHIC

We present the results for the measurement of $\phi$ meson production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au and pp collisions at the Relativistic Heavy Ion Collider (RHIC). Using the event mixing technique, spectra and yields are obtained from the $\phi\to K^{+}K^{-}$ decay channel for different centrality bins in Au+Au collisions and in pp collisions. We observe that the spectrum shape in Au+Au collisions depends weakly on the centrality and the shape of the spectrum in pp collisions is significantly different from that in Au+Au collisions. In Au+Au collisions, the extracted yield of $\phi$ meson is flat as a function of rapidity; The $$ of $\phi$, extracted from the fit function to the spectra, shows a different behavior as a function of centrality than that of $\pi^-$, $K^-$ and $\bar{p}$Comment: Proceedings for the 7th International Conference on Strangeness in Quark Matte

Strongly Intensive Measures for Multiplicity Fluctuations

The recently proposed two families of strongly intensive measures of fluctuations and correlations are studied within Hadron-String-Dynamics (HSD) transport approach to nucleus-nucleus collisions. We consider the measures $\Delta^{K\pi}$ and $\Sigma^{K\pi}$ for kaon and pion multiplicities in Au+Au collisions in a wide range of collision energies and centralities. These strongly intensive measures appear to cancel the participant number fluctuations. This allows to enlarge the centrality window in the analysis of event-by-event fluctuations up to at least of 10% most central collisions. We also present a comparison of the HSD results with the data of NA49 and STAR collaborations. The HSD describes $\Sigma^{K\pi}$ reasonably well. However, the HSD results depend monotonously on collision energy and do not reproduce the bump-deep structure of $\Delta^{K\pi}$ observed from the NA49 data in the region of the center of mass energy of nucleon pair $\sqrt{s_{NN}}= 8\div 12$ GeV. This fact deserves further studies. The origin of this `structure' is not connected with simple geometrical or limited acceptance effects, as these effects are taken into account in the HSD simulations

Hard and soft probe - medium interactions in a 3D hydro+micro approach at RHIC

We utilize a 3D hybrid hydro+micro model for a comprehensive and consistent description of soft and hard particle production in ultra-relativistic heavy-ion collisions at RHIC. In the soft sector we focus on the dynamics of (multi-)strange baryons, where a clear strangeness dependence of their collision rates and freeze-out is observed. In the hard sector we study the radiative energy loss of hard partons in a soft medium in the multiple soft scattering approximation. While the nuclear suppression factor $R_{AA}$ does not reflect the high quality of the medium description (except in a reduced systematic uncertainty in extracting the quenching power of the medium), the hydrodynamical model also allows to study different centralities and in particular the angular variation of $R_{AA}$ with respect to the reaction plane, allowing for a controlled variation of the in-medium path-length.Comment: 5 pages, 4 figures, Quark Matter 2006 proceedings, to appear in Journal of Physics

Probing jet properties via two particle correlation method

The formulae for calculating jet fragmentation momentum, $$, and parton transverse momentum,$$, and conditional yield are discussed in two particle correlation framework. Additional corrections are derived to account for the limited detector acceptance and inefficiency, for cases when the event mixing technique is used. The validity of our approach is confirmed with Monte-carlo simulation.Comment: Proceeding for HotQuarks2004 conference. 11 pages, 8 figures, corrected for typo

Space-time analysis of reaction at RHIC

Space-time information about the Au-Au collisions produced at RHIC are key tools to understand the evolution of the system and especially assess the presence of collective behaviors. Using a parameterization of the system's final state relying on collective expansion, we show that pion source radii can be tied together with transverse mass spectra and elliptic flow within the same framework. The consistency between these different measures provide a solid ground to understand the characteristics of collective flow and especially the possible peculiar behavior of particles such as Xi, Omega or phi. The validity of the short time scales that are extracted from fits to the pion source size is also addressed. The wealth of new data that will soon be available from Au-Au collisions at sqrt{s_{NN}} = 200 GeV, will provide a stringet test of the space-time analysis framework developped in these proceedings.Comment: Invited talk given at the SQM2003 conference (March 2003), to be published in Journal of Physics G. 10 pages, 3 figure

Heavy flavor production in pA collisions

Heavy quark production in high-energy proton-nucleus (pA) collisions is described in the framework of the Color Glass Condensate. kT factorization is broken even at leading order albeit a more general factorization in pA holds at this order in terms of 2, 3 and 4 point correlators of Wilson lines in the nuclear target. The x-evolution of these correlators is computed in the large A and large N mean field limit of the Balitsky-Kovchegov equation. We show results for heavy quark production at RHIC and LHC energies.Comment: Talk given at QM2006. 4