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Incident-energy and system-size dependence of directed flow

Introduction to directed flow Detectors: ZDC-SMD, (F)TPC Cross check with PHOBOS Comparison between 4 systems Summary. Incident-energy and system-size dependence of directed flow. Gang Wang (UCLA) for STAR Collaboration. < px> or directed flow. rapidity. p t. Directed flow ( v 1 ).

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Incident-energy and system-size dependence of directed flow

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  1. Introduction to directed flow • Detectors: ZDC-SMD, (F)TPC • Cross check with PHOBOS • Comparison between 4 systems • Summary Incident-energy and system-size dependence of directed flow Gang Wang (UCLA) for STAR Collaboration

  2. <px> or directed flow rapidity pt Directed flow (v1) Anisotropic flow Elliptic flow (v2) Higher harmonics Gang Wang (UCLA) Nov 19, 2006

  3. Non-flow effects Flow fluctuations Low statistics Harder! Easier to measure RHIC J. -Y. Ollitrault, Nucl. Phys. A638, 195c (1998). STAR Collaboration, Phys. Rev. Lett. 92, 062301 (2004) Gang Wang (UCLA) Nov 19, 2006

  4. STAR Main Detector Gang Wang (UCLA) Nov 19, 2006

  5. STAR ZDC-SMD • New knowledge of the direction of the impact parameter vector • Minimal, if any, non-flow effects • Worse resolution than from TPC, but that disadvantage is minor ZDC side view SMD is 8 horizontal slats & 7 vertical slats located at 1/3 of the depth of the ZDC Scintillator slats ofShower Max Detector Transverse plane of ZDC Gang Wang (UCLA) Nov 19, 2006

  6. Cross check with PHOBOS PHOBOS Collaboration, Phys. Rev. Lett. 97, 012301 (2006) 5% -40% Within errors, STARv1 of charged hadrons agrees with PHOBOS’ results. Gang Wang (UCLA) Nov 19, 2006

  7. Comparisons of charged hadron v1between 4 collision systems:200 GeV Au +Au200 GeV Cu +Cu 62.4 GeV Au +Au 62.4 GeV Cu +Cu Gang Wang (UCLA) Nov 19, 2006

  8. Resolution of 1st-order event plane from STAR ZDC-SMD Full EP resolution depends on spectator v1 and the number of hits falling on ZDC-SMDs. Gang Wang (UCLA) Nov 19, 2006

  9. Best case: 200 GeV Au + Au Charged hadron v1 is in the direction opposite to that of spectators. Gang Wang (UCLA) Nov 19, 2006

  10. Best case: 200 GeV Au + Au In mid-rapidity, v1(pt) crosses zero at pt above 1 GeV/c in the central and mid-central collisions. Not seen in the forward region. Hydro model predicts the zero-crossing in v1(pt), but the prediction also applies to the forward region. If we assume that pions and protons flow oppositely, then the change in their relative abundances leads to the zero-crossing. With the yields of (anti)proton and pion, we can fit the v1(pt) points assuming v1(pt) for pions and (anti)protons are straight lines. Gang Wang (UCLA) Nov 19, 2006

  11. AMPT v1(η): system-size dependence System size doesn’t seem to influence v1(η). Gang Wang (UCLA) Nov 19, 2006

  12. v1(η): incident-energy dependence v1 magnitude is bigger at 62.4 GeV than at 200 GeV. The hypothesis of limiting fragmentation is supported. Gang Wang (UCLA) Nov 19, 2006

  13. v1(pt) At 200 GeV,v1(pt)shows similarity in Au +Au and Cu +Cu collision systems. At 62.4 GeV, this is true for low pt. More statistics is needed in higher ptfor Cu +Cu. For all 4 cases, v1(pt)goes to zero when pt is zero, and increases in magnitude with pt until reaching the maximum and turning back. Gang Wang (UCLA) Nov 19, 2006

  14. Integrated v1 At 200 GeV, integrated v1 shows similarity in Au +Au and Cu +Cu collision systems. At 62.4 GeV, this is seemingly true. More statistics is needed for Cu +Cu. For all 4 cases, integratedv1goes to zero in central collisions, and increases in magnitude from central to peripheral collisions. Gang Wang (UCLA) Nov 19, 2006

  15. Summary • Best case: 200 GeV Au + Au • Charged particlev1(η) tends to turn back towards zero at forward pseudo-rapidities in central collisions. • v1(pt) crosses zero at pt above 1 GeV/c in central and mid-central collisions in mid-rapidities. • v1 shows similiarities between AuAu and CuCu as functions of η, pt and centrality at both 200 GeV and seemingly at 62.4 GeV. • AMPT model predicts this effect at 200 GeV. • Limiting fragmentation hypothesis is supported by AuAu data, and seemingly by CuCu data. • Results of v1{ZDC-SMD} will be cross-checked by other methods. Gang Wang (UCLA) Nov 19, 2006

  16. Backup Slides Gang Wang (UCLA) Nov 19, 2006

  17. Flow study with ZDC-SMD: 4 terms In analysis: To systematically study the method with ZDC-SMD, we can use the sub event plane from only east or west ZDC-SMD, instead of the full event plane, and even break down the correlation into X and Y direction. For example: Definitions of 4 terms: Gang Wang (UCLA) Nov 19, 2006

  18. Identified particles : v1 in 62 GeV Au +Au STARCollaboration, Phys. Rev. C 73, 034903 (2006) Gang Wang (UCLA) Nov 19, 2006

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