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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 STAR experiment Results and discussions Partonic collectivity NQ Scaling Ideal Hydrodynamic

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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 • STAR experiment • Results and discussions • Partonic collectivity • NQ 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

  5. STAR Detector TOF TPC FTPC Full azimuthal particle identification! e, π, ρ, K, K*, p, φ, Λ, Δ, Ξ, Ω, D, ΛC, J/ψ …

  6. Particle Identification 200 GeV Au + Au collisions • Reconstructed by decay topology • Daughter hadrons are identified by dE/dx in TPC • Signal to background ratio ~ 1 – 20 (depends on colliding system, particle type and pT) STAR preliminary

  7. Partonic Collectivity 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!

  8. 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 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)...

  9. NQ Scaling in Small System STAR preliminary • NQ scaling works, up to pT/nq =1.3~1.5 GeV/c, in 200 GeV Cu + Cu collisions at RHIC within errors PHENIX π, K and p: arXiv:0805.4039

  10. 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)

  11. 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)

  12. Hydro Test (I) Ideal hydro: P. Huovinen, private communication Au+Au at 200 GeV • Ideal hydro fails to reproduce the data. • Fluctuation of v2? Viscosity ? Incomplete thermalization ?

  13. Hydro Test (II) 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

  14. Ideal Hydro Limit STAR preliminary STAR preliminary Hydro limit ΞΛp 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)

  15. Effective η/s Extracted from Model STAR preliminary • Data shows particle type dependence, not a built-in feature in the model • Can viscous hydrodynamics explain the particle type dependence ? • Inferred η/s depends strongly on the eccentricity model Caveats: Transport model motivated ~ best for dilute system of massless particles no phase transition T: π spectra slope 200 MeV R: Glauber or CGC calculation H. J. Drescher et al, PRC 76 024905 (2007)

  16. The World Collection of η/s STAR preliminary See M. Sharma’s talk for pT correlation at QM 09

  17. Summary • Confirm Partonic collectivity. • NQ scaling: (a) In Au + Au collisions, Protons, probably Λ start deviating from the scaling at large pT; (b) In Cu + Cu collisions, works up to pT/nq = 1.3~1.5 GeV/c. • Ideal hydrodynamics test: (a) Fails to reproduce the centrality dependence of v2. (b) v4/v22larger than ideal hydro prediction. • Ideal hydro limit (a) A model dependent fit shows that the system has not reached the hydro limit. (b) Inferred η/s shows particle type and eccentricity model dependence.

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