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Directed flow of identified particles from Au+Au Collisions at RHIC

Directed flow of identified particles from Au+Au Collisions at RHIC. Jiayun Chen (for the STAR Collaboration) Institute of Particle Physics, Wuhan, P.R. China Brookhaven National Lab. Outline. Motivation Data sample, Proton selections, & V0 reconstruction

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Directed flow of identified particles from Au+Au Collisions at RHIC

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  1. Directed flow of identified particles from Au+Au Collisions at RHIC Jiayun Chen (for the STAR Collaboration) Institute of Particle Physics, Wuhan, P.R. China Brookhaven National Lab.

  2. Outline • Motivation • Data sample, Proton selections, & V0reconstruction • Event plane reconstruction • v1 results • Discussion and Summary SQM07 June. 24.

  3. <px> or directed flow rapidity pt Motivation Directed flow (v1) Anisotropic flow Elliptic flow (v2) Higher harmonics SQM07 June. 24.

  4. flow antiflow Motivation Anti-flow/3rd flow component, with QGP  v1 flat at middle rapidity. Directed flow (v1) and phase transition Brachmann, Soff, Dumitru, et. al. , PRC 61 (2000) 024909. L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002) SQM07 June. 24.

  5. Common cut: |Primary Vertex| < 30cm No. Dedx Points > 10 No. fit Points > 20 No. fit Points/No. Max [0.52,1.05] Global DCA < 1.0cm nSigma [-2.5,2.5] Proton: 0.4 < pT <1.0 (GeV/c) Antiproton: 0.15< pT <1.0 (GeV/c) DataSet: 62GeV Au+Au Minimum Bias 200GeV Au+Au Minimum Bias Proton & Antiproton Selection STAR Preliminary SQM07 June. 24.

  6. cuts: Distance of closest approach(DCA) between daughters < 0.8cm DCA of V0 to Primary Vertex (PV) < 0.5cm Daugter’s DCA to PV > 0.8 cm decay length > 6.0cm daughter’s Tpc Hits > 15 V0sreconstruction 1.11<mass<1.12 0.48<mass<0.51 1.11<mass<1.12 SQM07 June. 24.

  7. Event Planereconstruction the event plane vector and the event plane angle from the nth harmonic of the particle’s azimuthal distribution are defined by the equations: -- the azimuthal angle of the ith particle in the event plane determination -- weights SQM07 June. 24.

  8. Flattening Event Plane FTPC Raw Phi distribution Principle of shifting: Make corrections to the event plane angle itself, & flatten the event plane distribution. The corrected event plane angle is FTPC weighed Psi distribution E877 Collaboration, J. Bareeette et al, Phys.Rev.Lett.70,2996(1993) SQM07 June. 24.

  9. Event Plane FTPC Event Plane distribution ZDCSMD Event Plane distribution SQM07 June. 24.

  10. Combined Event Plane • After the flattening of YFTPC & YZDCSMD Full EP. The final event plane used is defined by the sum of Where • or weight is from resolution SQM07 June. 24.

  11. Resolution of FTPC,ZDCSMD,{FTPC,ZDCSMD}(62GeV Au+Au) STAR Preliminary The event plane resolution is enhanced by combining EP of FTPC & ZDC-SMD with proper weight. SQM07 June. 24.

  12. Proton & Antiproton v1vs. Rapidity(62GeV) STAR Preliminary STAR Preliminary 30%-60% 30%-60% with combined RP • Proton 0.4<pT<1.0 (GeV/c) • v1=ay dv1/dy = -0.4± 1.1 • Antiproton 0.15<pT<1.0 (GeV/c) • v1=ay dv1/dy = 1.3± 1.5 • Proton v1 is less than 1%, • Antiproton v1 is less than 2%. SQM07 June. 24.

  13. Resolution of FTPC,ZDCSMD,{FTPC,ZDCSMD}(200GeV Au+Au) Because the directed flow moves to larger pseudo-rapidity at the higher beam energy, the FTPC is less useful. no obvious improvement for combined event plane at 200GeV. SQM07 June. 24.

  14. Proton & Antiproton v1vs. Rapidity(200GeV) 30%-60% STAR Preliminary with {ZDC-SMDs} RP • Proton 0.4<pT<1.0 (GeV/c) • v1=ay dv1/dy = -1.9± 0.8 • Antiproton 0.15<pT<1.0 (GeV/c) • v1=ay dv1/dy = -0.6± -1.0 • Proton v1 is less than 1%, • Antiproton v1 is less than 2%. SQM07 June. 24.

  15. Proton & Antiproton v1vs. Centrality STAR Preliminary STAR Preliminary • v1(proton & antiproton) at 62GeV have weak centrality dependence. 62GeV combined RP 200GeV ZDC-SMDs RP SQM07 June. 24.

  16. Ks v1vs. Rapidity(62GeV) STAR Preliminary v1=ay dv1/dy =-3.2±1.7 SQM07 June. 24.

  17. L & Lv1vs. Rapidity(62GeV) STAR Preliminary STAR Preliminary Work in progress. SQM07 June. 24.

  18. Summary • The event plane resolution is enhanced by combining EP of FTPC & ZDC-SMD with proper weight; • Au+Au at 62.4GeV & 200GeV • Proton v1 is less than 1%. • AntiProton v1 is less than 2%. • Weak centrality dependence at 62GeV. • Made an attempt to studydirected flow of K0S & L, L. • Looking forward to analyzing run VII’s data (~60M MB events). SQM07 June. 24.

  19. Backup

  20. STAR ZDC-SMD ZDC side view SMD is 8 horizontal slats & 7 vertical slats located at 1/3 of the depth of the ZDC Transverse plane of ZDC Scintillator slats ofShower Max Detector • 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 SQM07 June. 24.

  21. Motivation RQMD v2.4 Positive space-momentum correlation, no QGP necessary  v1 wiggle. Directed flow (v1) and baryon stopping R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000) SQM07 June. 24.

  22. Motivation (GeV) • freeze-out of multi-strange hadrons - at higher temperature Tfo - with lower collective velocity T • less interaction of strange hadrons with non-strange hadrons • sensitivity to the early, partonic stage Nucl. Phys. A757, 102 (2005) SQM07 June. 24.

  23. SQM07 June. 24.

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