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v 2 and v 4 centrality, p t and particle-type dependence in Au+Au collisions at RHIC

v 2 and v 4 centrality, p t and particle-type dependence in Au+Au collisions at RHIC. Yuting Bai for the STAR Collaboration. Outline. Introduction v 2 v 4 v 4 /v 2 2 Conclusion. Anisotropic Flow. Anisotropic flow ≡ azimuthal correlation with the reaction plane

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v 2 and v 4 centrality, p t and particle-type dependence in Au+Au collisions at RHIC

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  1. v2 and v4 centrality, pt and particle-type dependence in Au+Au collisions at RHIC Yuting Bai for the STAR Collaboration

  2. Outline • Introduction • v2 • v4 • v4/v22 • Conclusion Yuting Bai

  3. Anisotropic Flow • Anisotropic flow ≡ azimuthal correlation with the reaction plane • established early, self-quenching, therefore sensitive to the early stage of the collisions Yuting Bai

  4. Charged particle v2 from four particle cumulant are measured up to ~ 10 GeV at 200GeV. For Au+Au at 200 GeV still significant v2 above 6 GeV/c -1.3 < h < 1.3 Star Preliminary Star Preliminary Charged particle v2 as function of pt at 200GeV and 62GeV v2{4}: v2 from 4-particle cumulant method. Yuting Bai

  5. Star Preliminary Star Preliminary Charged particle v2 as function of pt at 200GeV and 62GeV • The centrality dependence of v2 changes from low-pt to intermediate pt. • At intermediate pt the maximum v2 is for the 30-40% centrality bin around 3 GeV/c. Yuting Bai

  6. v2 increases from 62 to 200 GeV Star Preliminary Charged particle v2 as function of pseudorapidity at 200GeV and 62GeV Yuting Bai

  7. Star Preliminary v2{200}/v2{62} as function of pseudorapidity at 200GeV and 62GeV • The increase in v2 from 62 GeV to 200 GeV is larger at forward rapidity • could be understood as a result of v2 ~ dN/dh Yuting Bai

  8. Star Preliminary Charged particle v2 as a function of h-ybeam at 200GeV and 62GeV • Longitudinal scaling approximately holds Only particles with positive h are shown Yuting Bai

  9. Star Preliminary Centrality dependence: (mT – m) scaling • At low-pt mT-scaling: indicative for a common velocity for the different particles • At intermediate pt meson-baryon grouping: indicative for coalescence mechanism • mT-scaling and baryon meson grouping holds for all centralities! event plane method Yuting Bai

  10. Centrality dependence: NQ scaling Star Preliminary • NQ scaling holds for all centralities. •  is systematically lower than other particles in central collisions. Yuting Bai

  11. Star Preliminary Star Preliminary NQ scaling at 62.4GeV • At 62.4 and 200 GeV the same scaling is observed! minbias data (0-80%) Yuting Bai

  12. Higher Harmonics Peter Kolb, PRC 68, 031902 • Higher harmonics are expected to be present. For smooth azimuthal distributions they will be small, vn ~ v2n/2 • v4 /v22 a probe of ideal hydro behavior and related to degree of thermalization! R.S.Bhalerao et.al PLB 627,49; Borghini and Ollitrault, arXiv:nucl-th/0506045 Yuting Bai

  13. Charged particle v4 as function of pt at 200GeV and 62GeV Star Preliminary Star Preliminary -1.3 < eta < 1.3 Relative to the 2nd order event plane • Charged particle v4 are measured up to ~ 7 GeV at 200GeV. Yuting Bai

  14. Star Preliminary Charge particle v4 as function of pseudorapidity at 200GeV and 62GeV • As for v2, v4 increases from 62 to 200 GeV Yuting Bai

  15. Star Preliminary Charged particle v4 as function of h-ybeam at 200GeV and 62GeV • Same as v2, for v4 longitudinal scaling approximately holds Yuting Bai

  16. v4 systematic uncertainty estimate • Uncertainties on <v4> are small, however they quickly become significant at larger pt Yuting Bai

  17. Star Preliminary v4/v22 for charged particles at 200GeV • v4 /v22 a detailed probe of ideal hydro behavior and related to the degree of thermalization! • Data points are above the model predictions, however due to the systematic uncertainty from non-flow we can not exclude the models yet Yuting Bai

  18. Conclusions • v2 from four particle cumulant is measured up to 10 GeV/c • Still significant v2 observed above 6 GeV/c • v2 for identified particles shows mT scaling at low-pt and NQ scaling at intermediate pt • For all centralities • The energy dependence of v2 and v4 is approximately described by longitudinal scaling • The observed ratio of v4/v22 is above the ideal hydro predictions and close to AMPT, however the systematic uncertainties from non-flow do not allow us to contradict ideal hydrodynamics Yuting Bai

  19. v4/v22 for charged particle as a function of pt at 200GeV and 62GeV Star Preliminary Yuting Bai

  20. v4/v22 for charged particles as function of pseudorapidity at 200GeV and 62GeV Star Preliminary Yuting Bai

  21. v4/v22 for charged particles as a function of pseudorapidity at 200GeV • Systematic errors are shown at mid-rapidity only. At forward rapidity, the non-flow effects are expected to be small. • at mid-rapidity, the ratios are above 1, which is compatible with those at forward rapidity . Star Preliminary Yuting Bai

  22. non-flow effect on v4/v22 For v4/v22 : Yuting Bai

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