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Elliptic Flow at RHIC

Elliptic Flow at RHIC. U.S. Labs: Argonne, Berkeley, Brookhaven National Labs U.S. Universities: Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY,

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Elliptic Flow at RHIC

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  1. Elliptic Flow at RHIC U.S. Labs: Argonne, Berkeley, Brookhaven National Labs U.S. Universities: Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Yale Brazil Universidade de Sao Paolo China IHEP - Beijing, IPP - Wuhan STAR Collaboration England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt Poland: Warsaw University Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvino

  2. Geometry of STAR Magnet Time Projection Chamber Coils SiliconVertexTracker TPC Endcap & MWPC FTPCs ZDC ZDC VertexPositionDetectors Endcap Calorimeter Central Trigger Barrel or TOF BarrelEMCalorimeter RICH Year 1: Magnet, TPC, CTB, ZDC, RICH

  3. STAR TPC • Active volume: • Cylinder R=2 m, L=4 m • 139,000 electronics channels • 512 time buckets each • cosmic ray event in the TPC 

  4. Au on Au at CM Energy ~ 130 AGeV Data Taken June 25, 2000. Pictures from online display.

  5. Data set • Minimum bias trigger - Zero Degree Calorimeter coincidence • Magnetic field 0.25 tesla • pt > 75 MeV/c • 22k events with reconstructed vertex • | Zvertex | < 75 cm, | Xvertex | < 1 cm, | Yvertex | < 1 cm • Quality cuts for flow analysis • 0.1 < pt < 2.0 GeV/c -- to have efficiency constant +/- 10% • || < 1.3

  6. Vertex finder and tracking efficiencies All events Beam-gas interactions Beam-gas interactions CTB trigger threshold Correlation between Central Trigger Barrel signal and number of primary tracks => near constant tracking efficiency Reconstructed vertex CTB trigger threshold

  7. Elliptic Flow Y • Rescattering • Converts space to momentum anisotropy • Becomes more spherical • Self-quenching X => Early time physics Zhang, Gyulassy, Ko, PL B455 (1999) 45 Elliptic flow XZ-plane - the reaction plane t (fm/c)

  8. Azimuthal Anisotropy Elliptic flow: pY Event Plane - an estimator for the reaction plane f i pX

  9. Method Summary • Define subevents - independent groups of particles • Correlate subevent planes • Calculate the reaction plane resolution • Correlate particles with a plane • Gives v(, pt) • Correct for the reaction plane resolution

  10. Quality Check: Some Details Particle Correlation with respect to event plane Particle f distribution in the lab Event plane distribution TPC sector boundaries Note: Highly suppressed zero (fluctuations ~3%)

  11. Centrality • nch - number of primary tracks in |h| < 0.75 • ~ 90% ofall hadronic Au+Au interactions • Eight centrality bins

  12. The Signal A B A B 2nd harmonic • Non-Flow Effects • Momentum conservation • HBT, Coulomb (final state) • Resonance decays • Jets (jet quenching -- flow !) 1st harmonic -1<<-0.05 0.05<<1 • Subevents chosen • Pseudorapidity • Random • Charge First and higher harmonics => systematic error for elliptic flow

  13. Centrality Dependence Subevents chosen: - Pseudorapidity - Random - Charge •  = initial space anisotropy= y2 - x2/y2 + x2 • Curve for v2 /  = 0.16 • Systematic error: 0.005 • Uncertainty of 10% in stotal => 5% in b/2R Particles correlated: - In opposite hemisphere - From all other particles - Opposite charge Cuts:

  14. Minimum Bias (average over 8 centrality bins, weighted with nch) pseudorapidity transverse momentum GeV/c

  15. Summary • v2 increases with collision energy • AGS (full energy) 2% • SPS 3.5% • RHIC 6% • Comparison with theory • Data: v2,max  0.06 • RQMD: v2,max  0.025, different centrality dependence • UrQMD: v2,max  0.015 • Data: v2 / 0.16 - 0.17 • Hydro: v2 /  0.19 - 0.25

  16. Conclusions • Elliptic flow is large at RHIC, v2,max  0.06 • Reaction plane resolution is good for related studies • v2() constant for || < 1.3 • v2(pt) almost linear up to 2 GeV/c • stronger than average radial in-plane expansion • Centrality dependence close to hydrodynamic model • Magnitude approaching hydrodynamic model prediction • Consistent with significant early-time equilibration

  17. Anisotropic flow: Next • Flow of identified particles • Flow of high pt particles • Directed flow p K d  e

  18. v2 Theory Hydro: P.F. Kolb, et al RQMD v2.4 v2 /  SPS 40 GeV/A SPS RHIC 160 GeV/A b (fm)

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