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Event Anisotropy at STAR

Event Anisotropy at STAR. Na Li for the STAR collaboration Brookhaven National Laboratory Institute of Particle Physics, Central China Normal University. Outline. Introduction Results and discussions Partonic collectivity N umber of Q uarks Scaling Ideal Hydrodynamic Summary.

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Event Anisotropy at STAR

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  1. Event Anisotropy at STAR Na Li for the STAR collaboration Brookhaven National Laboratory Institute of Particle Physics, Central China Normal University

  2. Outline • Introduction • Results and discussions • Partonic collectivity • Number of Quarks Scaling • Ideal Hydrodynamic • Summary

  3. Physics Goals at RHIC • Identify and study the properties • of the matter (EOS) with partonic • degrees of freedom. • - Explore the QCD phase diagram. Hydrodynamic Flow Collectivity Local Thermalization = 

  4. hadronic partonic Elliptic Flow (v2) pressure gradient  collective flow Coordinate-Space Anisotropy Momentum-Space Anisotropy interactions • Elliptic flow: information about the early stage collision dynamics • Strange hadron: less sensitive to hadronic rescattering • Good probe of the early stage of the collision D, , Ω, Ξ, Λ, , K, p

  5. STAR Detector Full Azimuthal TOF • Time Projection Chamber: • Main TPC: • |η| < 1; • Time Of Flight: • Particle identification • Forward TPC: • 2.5 < |η| < 4.0; • Rapidity gap could reduce “non-flow” effects; • Zero Degree Calorimeter: • |η| > 6.0; TPC ZDC (SMD) FTPC

  6. Partonic Collectivity Open points: PHENIX π and p: nucl-ex/0604011v1 NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004) 328-332 Final word on partonic collectivity at RHIC!

  7. NQ Scaling at Large pT Ideal hydro: P. Huovinen and P. V. Ruuskanen, Annu. Rev. Nucl. Part. Sci. 56, 163 (2006) and private communication • Centrality: 0 - 80% • Systematic uncertainties • FTPC event plane • NQ Scaling • Protons , probably Λ too, start deviating from the scaling at large pT STAR preliminary D. Molnar and S. Voloshin, PRL91, 092301 (2003) R. J. Fries et. al., PRC68, 044902 (2003) V. Greco et. al, PRC68, 034904 (2003) J. Jia and C. Zhang, PRC75, 031901(R) (2007)... Narrow band: 5% v2 non-flow for reconstructed particles Wide band: 15% v2 non-flow for π and p

  8. Energy Dependence • v2 in Cu + Cu (Au +Au) at 200 and 62.4 GeV are comparable within statistical errors STAR preliminary v2 at Cu + Cu 62.4 GeV ~ 12.5 M events - Same procedure used for 200 GeV. - Event plane resolution is 0.088 ± 0.004 in 0 - 60 %, about factor 2 smaller than that in 200 GeV due to lower multiplicity. STAR Au + Au 200 GeV : PRC77, 054901 (2008) Au + Au 62.4 GeV : PRC75, 054906 (2007)

  9. System Size Dependence STAR preliminary Au + Au at 200 GeV • v2 scaled by eccentricity • Remove the initial geometry effect • v2 seems solely depending on initial geometry and number of participant in 200 GeV collisions • v2∝ v2(ε, Npart) Au + Au : PRC77, 054901 (2008)

  10. Ideal Hydro Test (I) Ideal hydro: P. Huovinen, private communication Au+Au at 200 GeV STAR preliminary Phys. Rev. C 77 (2008) 54901 • Ideal hydro fails to reproduce the data. • Fluctuation of v2? Viscosity ? Incomplete thermalization ?

  11. Ideal Hydro Test (II) Au+Au at 200 GeV 0-80% Borghini & Ollitrault, PLB 642 227 (2006) • v4/v22 results suggest that ideal hydro limit is not reached • Need to study η/s to see how far away we are from ideal hydro limit

  12. Ideal Hydro Limit STAR preliminary Hydro limit ΞΛ K h STAR preliminary • Ideal Hydro Limit • Even in central Au + Au collisions, fitting results indicate that the system is still away from hydro limit v2/ε scaling: S. Voloshin (for STAR Collaboration), J.Phys.G34(2007)S883 PHENIX π, K and p: nucl-ex/0604011v1 CGC eccentricity: H.J. Drescher and Y. Nara, PRC 76 041903 (2007), H.J. Drescher and Y.Nara, PRC 75 034905 (2007)

  13. Hunting the Perfection Effective η/s from transport model motivated approach STAR preliminary η/s(CGC) < η/s(Glauber) Includes hadronic effect – Large η/s Caveats : Transport model motivated – best for dilute system No phase transition Averaged over all phases – effective quantity

  14. Summary • Partonic collectivity at RHIC demostrated! Test of local thermalization is the next step. • NQ scaling: In Au + Au collisions, p and Λ start deviating from the scaling at large pT. The scaling seems also work in Cu+Cu collisions. • Ideal hydrodynamic predictions test: (a) Hydro fails to reproduce the centrality dependence of v2. (b) v4/v22datalarger than ideal hydro prediction. • Ideal hydro limit (a) A model dependent fit shows that the system has not reached the hydro limit. (b) Heavier particles are closed to hydro limit. (c) η/s is a few times of the conjectured quantum limit.

  15. Backup

  16. Transport Model Approach hydro limit • Knudsen number • degrees of equilibration • Reach hydro limit when K 0 • Transport model results (symbols) can be reproduced by the formula below • K0 = 0.7, cs2 = 1/3 v2 C. Gombeaud and J.-Y. Ollitrault, PRC77, 054904 (2008) Knudsen number K σ : parton cross section cs : speed of sound S : transverse area (obtained by Glauber MC)

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