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What have we learned from Anisotropic Flow at RHIC ?

What have we learned from Anisotropic Flow at RHIC ?. Hiroshi Masui for the PHENIX Collaboration 2006 RHIC & AGS Annual User’s meeting June 5 – 9, 2006 at Brookhaven National Laboratory Workshop 8 : How perfect is this matter ?. “Perfect liquid” at RHIC.

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What have we learned from Anisotropic Flow at RHIC ?

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  1. What have we learned from Anisotropic Flowat RHIC ? Hiroshi Masui for the PHENIX Collaboration 2006 RHIC & AGS Annual User’s meeting June 5 – 9, 2006 at Brookhaven National Laboratory Workshop 8 : How perfect is this matter ? Hiroshi Masui / University of Tsukuba

  2. “Perfect liquid” at RHIC • Strong collective flow, nearly perfect liquid Hiroshi Masui / University of Tsukuba

  3. Definitions Pz Py Z • Anisotropic Flow • Azimuthal correlation to reaction plane • Elliptic flow (v2) Px Reaction plane Y X Hiroshi Masui / University of Tsukuba

  4. Outline • Elliptic Flow and Hydrodynamics • PHENIX experiment • Particle identification, event plane • Eccentricity scaling and speed of sound • Kinetic energy (Hydro) scaling and Partonic collectivity • Summary Hiroshi Masui / University of Tsukuba

  5. v2 and hydrodynamics PHENIX : PRL 91, 182301 (2003) D. Teaney : PRC 68, 034913 (2003) • Large elliptic flow at RHIC • Elliptic flow is well described by hydrodynamics • Magnitude, particle type up to pT ~ 1.5 GeV/c • Indicate early thermalization  < 1 fm/c, extremely low viscosity < 0.1 Hiroshi Masui / University of Tsukuba

  6. PHENIX experiment • Hadron identification • Time-of-Flight • || < 0.35, || < /4 • EM Calorimeter • || < 0.35, || < /2 • Event plane • Beam Beam Counter, 3 < || < 3.9, full azimuth Hiroshi Masui / University of Tsukuba

  7. Hadron identification • Time-of-flight • || < /4, || < 0.35 • Timing resolution ~ 120 ps • /K separation ~ 2 GeV/c • K/p separation ~ 4 GeV/c • Good timing resolution • EM Calorimeter • || < /2, || < 0.35 • Timing resolution ~ 400 ps • /K separation ~ 1 GeV/c • K/p separation ~ 2 GeV/c • Large acceptance Hiroshi Masui / University of Tsukuba

  8. Event plane @ 3<||<4 • Large rapidity gap • Central arm || < 0.35 BBC 3 < || < 4 • Smaller non-flow contribution Hiroshi Masui / University of Tsukuba

  9. v2 from ideal fluid dynamics cs = 1/3 t0 = 0.6 fm/c b = 8 fm • v2 scales initial eccentricity () • v2/ is independent on system size R • v2 grows with cs • Can we test these relations from the data ? transverse size of system R. S. Bhalerao, J.P. Blaizot, N. Borghini, J.-Y. Ollitrault, PLB 627, 49, (2005) Hiroshi Masui / University of Tsukuba

  10. Can we test eccentricity scaling of v2 ? • Does v2 scale eccentricity ? • Centrality dependence of v2/ • Is v2/ independent of system size ? • Au+Au vs Cu+Cu • Estimate of speed of sound can be made from the measurement of v2/ Hiroshi Masui / University of Tsukuba

  11. Eccentricity and integrated v2 • Eccentricity is usually estimated by Glauber Model • Integrated v2 is proportional to eccentricity • Advantage of integrated v2 : • Reduce large systematic error from Glauber MC, typically 20 – 30 % • Cancel systematic error from event plane determination Hiroshi Masui / University of Tsukuba

  12. Eccentricity scaling PHENIX PRELIMINARY • Scaling holds for a broad range of centrality • Centrality 30 -40 %, b ~ 8.7 fm • Independent of system size k ~ 3.1 obtained from data Hiroshi Masui / University of Tsukuba

  13. Estimate of cs v2/ @ <pT> ~ 0.45 GeV/c • Cs = 0.35  0.05 • Indicate softer EOS compared to cs=1/3 • v2/ ~ 0.1 (peripheral) – 0.2 (central) at STAR and PHOBOS • Integrated v2 does not develop so much in the late hadronic stage NOTE v2 value is typically factor 2 lager than Hiroshi Masui / University of Tsukuba

  14. Kinetic energy scaling M. Issah, A. Taranenko, nucl-ex/0604011 K0S,  (STAR) : PRL 92, 052302 (2004)  (STAR) : PRL 95, 122301 (2005) , K, p (PHENIX) : preliminary Meson v2 Baryon v2 • Kinetic energy scaling works up to KET ~ 1 GeV • Indicate hydrodynamic behavior • Possible hint of quark degrees of freedom at higher KET * Kinetic energy of a particle in a relativistic fulid KET ~ mT – m0 at y ~ 0 Hadron mass Hiroshi Masui / University of Tsukuba

  15. What can we learn from identified hadrons ? • NCQ (Number of Constituent Quark) scaling of v2 indicate partonic collectivity at RHIC •  meson is a good probe to test NCQ scaling • No re-scattering in hadronic stage • Longer life time ~ 40 fm/c • Thermal s-quark coalesce/recombine to form  meson QM2005, M. Oldenburg, STAR Hiroshi Masui / University of Tsukuba

  16. Clear  signal •   K+K- • Typical S/N ~ 0.3 • Centrality 20 – 60 % • S/N is good • Event plane resolution is good • Separation of v2 between meson and baryon is good • Magnitude of v2 do not vary very much Before subtraction Signal + Background Background After subtraction Hiroshi Masui / University of Tsukuba

  17.  Meson v2 • Obtained from invariant mass fit method • Consistent with standard subtraction method • Smaller systematic error • pT < 2 GeV/c • Consistent with mass ordering from hydrodynamics N. Borghini, J.-Y. Ollitrault, PRC 70, 064905 (2004) Hiroshi Masui / University of Tsukuba

  18. Partonic Collectivity (i) • Hydro + NCQ scaling works for  meson • STAR result favors NCQ=2 for  • Consistent with other multi-strange hadrons (, ) from STAR  Collective flow of s-quark Hydro. + Nquark scaling Hydro. (KET) scaling SQM2006, S. Blyth, STAR Hiroshi Masui / University of Tsukuba

  19. Partonic Collectivity (ii) PHENIX PRELIMINARY WWND 2006, M. Issah SQM2006, S. Esumi • Hydro + NCQ scaling describes v2 for a variety of particles measured at RHIC • Scaling breaks for higher pT Data :QM2005, PHENIX K0S,  (STAR) : PR 92, 052302 (2004)  (STAR) : PRL 95, 122301 (2005)  (STAR) : preliminary STAR preliminary 0-80% Au+Au 200GeV Yan Lu SQM05 P. Sorensen SQM05 M. Oldenburg QM05 K0S Hiroshi Masui / University of Tsukuba

  20. Summary • What have we learned from anisotropic flow + hydrodynamics at RHIC ? • Strongly interacting partonic matter • Large v2 Early thermalization,  < 1 fm/c • v2 scales eccentricity, independent of system size (Au, Cu) • Estimated speed of sound = 0.35  0.05 • Partonic Collectivity • Kinetic energy + NCQ scaling works for a broad set of particles • What more can be learned ? • Centrality, energy dependence of v2 • v4/(v2)2 as a probe for degree of thermalization • PHENIX talks in this session • 2:25 PM : S. Sakai, heavy flavor electron v2 • 4:20 PM : J. Newby, HBT Hiroshi Masui / University of Tsukuba

  21. Thank you Hiroshi Masui / University of Tsukuba

  22. Back up Hiroshi Masui / University of Tsukuba

  23. v2/, STAR, PHOBOS v2/part v2/ • v2/ ~ 0.1 – 0.2 CIPANP 2006, S. Voloshin, STAR QM2005, S. Manly, PHOBOS Hiroshi Masui / University of Tsukuba

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