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Anisotropic flow in AuAu and CuCu at 62 GeV and 200 GeV

This study examines the anisotropic flow (v1 and v2) in AuAu and CuCu collisions at 62 GeV and 200 GeV using the ZDC-SMD method. The results show centrality dependence and shed light on the direction and effects of flow and non-flow in these collisions.

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Anisotropic flow in AuAu and CuCu at 62 GeV and 200 GeV

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  1. Anisotropic flow in AuAu and CuCuat 62 GeV and 200 GeV Gang Wang (Kent State, Ohio)for theSTAR Collaboration • Introduction Flow Fourier coeffs (Oldenburg talk + others)  v1(y) structure ZDC upgrade Flow Study withZDC-SMD • Physics results  v1 in 62 GeV AuAu, 10% - 70% centrality  v1 in 62 GeV AuAu, centrality dependence  v1 in 200 GeV AuAu, centrality dependence  v2 in 200 GeV AuAu, 20% - 70% centrality  v2 in 200 GeV CuCu, 20% - 60% centrality  v2 in 200 GeV CuCu, centrality dependence • Summary

  2. v1(y) structure Models predict that anti-flow/3rd flow component, with QGP  v1(y) flat or a wiggle structure. J. Brachmann et al. PRC 61, 024909 (2000) L.P. Csernai, D. Rohrich PLB 458, 454 (1999) Gang Wang

  3. v1(y) structure Models without QGP also predict a wiggle structure in peripheral 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

  4. v1 - experimental complications Directed flow is small at RHIC, especially in the central rapidity region, and analyses are easily confused by non-flow effects (azimuthal correlations not related to the reaction plane orientation). To reduce sensitivity to non-flow [recent review in PRC 72, 014904 (2005)]: v1{3} -- the three-particle cumulant method; v1{EP1, EP2} -- the event plane method with mixed harmonics; v1{ZDC-SMD} -- the standard method with the 1st-order event plane determined from the sideward deflection (“bounce-off”)of spectator neutrons in the Shower Max detector (SMD) of the Zero Degree Calorimeters (ZDCs). Gang Wang

  5. 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

  6. 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

  7. Charged hadrons: v1 in 62 GeV Au +Au Au +Au 62 GeV STAR preliminary Models do well at larger |h| but their v1(h) is too flat near h=0 Gang Wang

  8. Charged hadrons : v1 in 62 GeV Au +Au STAR preliminary directed flow of charged particles is opposite to spectator bounce-off at all centralities, and three methods agree. Gang Wang

  9. NA49, Phys. Rev. C 68 (2003) 034903 Charged hadrons:v1 in 200 GeV Au +Au Au +Au 200 GeV STAR preliminary Similar trends in AuAu v1(h) vs. centrality from SPS thru top RHIC energy; 200 GeV central collisions allow v1 sign-change to be probed Gang Wang

  10. Au +Au 200 GeV STAR preliminary Charged hadrons: v2 in 200 GeV Au +Au Systematic check on v2 measurements using ZDC-SMD 1st harmonic event plane shows substantial non-flow effects in peripheral collisions. Gang Wang

  11. v2 – minimizing non-flow for CuCu analysis In this talk, we use this subset of elliptic flow analysis methods to reduce sensitivity to non-flow for CuCu [recent review in PRC 72, 014904 (2005)]: v2{4} -- four-particle cumulant; v2{AA-pp} -- the scalar product method; v2{qdist} -- involves fit to distribution of q = flow vector Q /√M ; the fit contains a term to account for non-flow. particle azim from given pt bin assume can be obtained from pp Sum over multiplicity, M Gang Wang

  12. Charged hadrons:v2 in 200 GeV CuCu v2 for CuCu is smaller than for AuAu but large relative size of CuCu non-flow & divergence among methods at higher pt requires further investigation Gang Wang

  13. Charged hadrons:v2 in 200 GeV CuCu Integrated v2(0.15 < pt < 2 GeV/c) again shows lower flow for CuCu & agreement on non-flow correction Gang Wang

  14. Summary • STAR ZDC-SMD allows the reaction plane to be determined with useful resolution from the “bounce-off” of spectator neutrons. This has been used to study charged particle v1 and v2 for 62 and 200 GeV AuAu & 200 GeV CuCu. • Charged particles in the h-region covered by the STAR TPC and FTPCs (up to |h| = 4.0) predominantly have opposite directed flow from the spectator nucleons. For 62 GeV AuAu, several models agree well in FTPC region, but their v1(h)is too flat at central pseudorapidities. • 62 & 200 GeV AuAu show a complex structure inv1 vs. h vs. centrality, and present a major challenge to models. 200 GeV central collisions allow v1 sign change near |h| = 3.5 to 4 to be probed. • For 200 GeV AuAu, v2{ZDC-SMD} allows nonflow-corrected elliptic flow to be extended to more peripheral centralities. • The relative importance of non-flow is greater for CuCu analysis than for AuAu – initial v2 estimates for 200 GeV CuCu based on v2{4}, v2{CuCu-pp}and v2{qdist} show reasonable consistency across broad regions of centrality and pT . Gang Wang

  15. Backup Slides Gang Wang

  16. Limiting Fragmentation in Au +Au 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. STAR preliminary The hypothesis holds here. ycm = 0 Gang Wang

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