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Directed Flow at RHIC Based on Transverse Deflection of Spectator Neutrons

Introduction to directed flow Detectors: ZDC-SMD, (F)TPC Method and check Comparison between 3 systems Summary. y. z. x. Directed Flow at RHIC Based on Transverse Deflection of Spectator Neutrons. Gang Wang (UCLA) for STAR Collaboration. < px> or directed flow. rapidity. p t.

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Directed Flow at RHIC Based on Transverse Deflection of Spectator Neutrons

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  1. Introduction to directed flow • Detectors: ZDC-SMD, (F)TPC • Method and check • Comparison between 3 systems • Summary y z x Directed Flow at RHIC Based onTransverse Deflection of Spectator Neutrons 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) Jun 7, 2006

  3. Hydro-dynamics model A . Nyiri, L.P. Csernai, et al., J. Phys. G31, S1045 (2005) v1(y) structure Models predict that anti-flow/3rd flow component, withQGP v1(y) flat or awigglestructure. J. Brachmann et al. PRC 61, 024909 (2000) L.P. Csernai, D. Rohrich PLB 458, 454 (1999) Gang Wang (UCLA) Jun 7, 2006

  4. v1(y) structure Models withoutQGP also predict awigglestructure inperipheral or mid-peripheral events. M. Bleicher and H. Stöcker, PLB 526, 309 (2002) RQMD Baryon stopping and positive space-momentum correlation UrQMD R. Snellings, H. Sorge, S. Voloshin, F. Wang, N. Xu, PRL 84, 2803 (2000); also H. Liu et al., PRC 59, 348 (1999). Gang Wang (UCLA) Jun 7, 2006

  5. Non-flow effects Flow fluctuations Low statistics Harder! Easier to measure RHIC Gang Wang (UCLA) Jun 7, 2006

  6. STAR Main Detector Gang Wang (UCLA) Jun 7, 2006

  7. STAR ZDC • Each of the RHIC experiments has a pair of Zero Degree Calorimeters for beam monitoring, triggering, and locating interaction vertices. • ZDCs detect neutrons emitted along beam directions and measure their total energy (multiplicity) . • Baseline ZDCs have no transverse segmentation, which motivates upgrade. Gang Wang (UCLA) Jun 7, 2006

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

  9. 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) Jun 7, 2006

  10. First result: cross check STARCollaboration, Phys. Rev. C 73, 034903 (2006) Au +Au 62 GeV Models do well at larger |h|but their v1(h) is too flat near h = 0 Gang Wang (UCLA) Jun 7, 2006

  11. Comparisons between 3 collision systems:62 GeV Au +Au200 GeV Au +Au200 GeV Cu +Cu Gang Wang (UCLA) Jun 7, 2006

  12. Au +Au 62 GeV 10% - 70% Au +Au 200 GeV Mid-rapidity AMPT model gives a Charged particle v1 is a monotonic function of η. Gang Wang (UCLA) Jun 7, 2006

  13. Hydro-dynamics model A . Nyiri, L.P. Csernai, et al., J. Phys. G31, S1045 (2005) Au +Au 62 GeV Forward rapidity AMPT model gives a AMPT model gives a AMPT model shows a similar tendency, with smaller magnitude. Gang Wang (UCLA) Jun 7, 2006

  14. Au +Au 200 GeV Hydro predicts the sign change in v1(pt) U. Heinz and P. Kolb, J. Phys. G30, S1229 (2004) p-bar flows with proton More Hydro? Assume (anti-)proton and pion v1(pt) are straight lines starting from zero, and neglect other particles. Charged particle v1(pt) can be fit simply. Gang Wang (UCLA) Jun 7, 2006

  15. Scaling behavior It has been observed that particle emission(both spectra and flow) as a function of rapidity in the vicinity of beam rapidity appears unchanged over a wide range of beam energies, a pattern known as limiting fragmentation. The hypothesis holds here. Gang Wang (UCLA) Jun 7, 2006

  16. 10% - 60% More Scaling STAR preliminary Gang Wang (UCLA) Jun 7, 2006

  17. Summary • For all 3 collision systems, charged particlev1(η) decreases with η in mid-rapitidies, flowing opposite to spectators. • Charged particlev1(η) approaches zero at forward η sooner or later. The more central collision, the sooner. • AMPT model predicts this effect, with much smaller magnitude. (cross-section?) • Hydro-dynamics model also predicts the zero-approaching. • Charged particle v1(pt) crosses zero at pt > 1 GeV/c in the TPC region at 200 GeV Au +Au. The more central collision, the sooner. • Hydro-dynamics model predicts the sign-change. • With an assumption of the straight-line shape in v1(pt) for identified particles, the slopes can be fit with particle yields. • Identified particle v1 still need more investigation. • Limiting fragmentation is observed when comparing 62 GeV and 200 GeV Au +Au. • System size doesn’t matter in v1? • 200 GeV Au +Au and Cu +Cu • Would look at 62 GeV Cu +Cu, and compare it with 62 GeV Au +Au. • v1results call for more input from model calculations. Gang Wang (UCLA) Jun 7, 2006

  18. Backup Slides Gang Wang (UCLA) Jun 7, 2006

  19. Identified particles : v1 in 62 GeV Au +Au STARCollaboration, Phys. Rev. C 73, 034903 (2006) Gang Wang (UCLA) Jun 7, 2006

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