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Elliptic Flow

Y. X. Elliptic Flow. Outline: Methods: - the use of many-particle correlations in many different approaches - non-flow and flow fluctuations Data: - centrality dependence at different energies - v 2 (p t ) at different energies

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Elliptic Flow

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  1. Y X Elliptic Flow Outline: Methods: - the use of many-particle correlations in many different approaches - non-flow and flow fluctuations Data: - centrality dependence at different energies - v2(pt) at different energies - v2(pt) of identified particles and fits to the blast wave model - v2(pt) at high pt. - azimuthal correlations at high pt’s. Models: - 2d and 3d hydro, hydro+RQMD - parton cascade model(s) (MPC, AMPT) - Color Glass Condensate (A. Krasnitz et al.) - Hadronic rescatterings ( T. Humanic) - … Speculations: - Constituent quark model - v2/ vs (dN/dy) /S

  2. Elab=40GeV 158 GeV NA45, QM’01 Preliminary STAR Preliminary SPS. Centrality dependence. v2 = 0.04 - Monotonically increases with the beam energy - Steeper centrality dependence at 158 GeV compared to 40 GeV ?

  3. Preliminary STAR STAR Preliminary Centrality dependence. RHIC. Note possible dependence on low pt cut 200 GeV: 0.2< pt < 2.0 130 GeV: 0.075< pt < 2.0 200 GeV: 0.150< pt < 2.0 4-part cumulants v2=0.05 200 GeV: Preliminary - Consistent results - At 200 GeV better pronounced decrease of v2 for the most peripheral collisions.

  4. v2 vs pseudorapidity; 3d hydro. 3d hydrodynamical calculations (boost invariant initial conditions) do not reproduce v2(); can the agreement be reached by modifying the initial conditions?

  5. STAR Preliminary v2(pt), non-flow vs pt • Non-flow contribution (on average) : • - about 7-10% at SPS, 160 GeV. • about 15% @ 130 GeV • about 20% @ 200 GeV • could slightly increase with transverse momentum

  6. v2(pbar) v2(p-,K-) baryons v2 mesons quarks v2(proton) v2(p+,K+) pt Preliminary Constituent quark model + coalescence coalescence fragmentation Low pt quarks High pt quarks Coalescence in the intermediate region (rare products): Side-notes: a) more particles produced via coalescence vs parton fragmentation  larger mean pt… b)  higher baryon/meson ratio - What is the centrality dependence of the effect?

  7. jet parton nucleon nucleon Jets at RHIC Find this……….in this p+p jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC)

  8. trigger Jets and two-particle azimuthal distributions p+p  dijet • trigger: highest pT track, pT>4 GeV/c • Df distribution: 2 GeV/c<pT<pTtrigger • normalize to number of triggers Phys Rev Lett 90, 082302 N.B. shifted horizontally by p/2 relative to previous STAR plots!

  9. Partonic energy loss in dense matter Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,… Multiple soft interactions: Gluon bremsstrahlung Opacity expansion: • Strong dependence of energy loss on gluon density glue: • measure DE color charge density at early hot, dense phase

  10. Leading hadron suppression Wang and Gyulassy: DE  softening of fragmentation  suppression of leading hadron yield Ivan Vitev, QM02

  11. Au+Au and p+p: inclusive charged hadrons nucl-ex/0305015 PhysRevLett 89, 202301 p+p reference spectrum measured at RHIC

  12. Suppresion of inclusive hadron yield RAA Au+Au relative to p+p RCP Au+Au central/peripheral nucl-ex/0305015 • central Au+Au collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT

  13. ? Azimuthal distributions in Au+Au Au+Au peripheral Au+Au central pedestal and flow subtracted Phys Rev Lett 90, 082302 Near-side: peripheral and central Au+Au similar to p+p Strong suppression of back-to-back correlations in central Au+Au

  14. ? Suppression of away-side jet consistent with strong absorption in bulk, emission dominantly from surface

  15. Is suppression an initial or final state effect? Initial state? Final state? partonic energy loss in dense medium generated in collision strong modification of Au wavefunction (gluon saturation)

  16. RCP nucl-ex/0305015 pQCD-I: Wang, nucl-th/0305010 pQCD-II: Vitev and Gyulassy, PRL 89, 252301 Saturation: KLM, Phys Lett B561, 93 Inclusive suppression: theory vs. data Final state Initial state pT>5 GeV/c: well described by KLM saturation model (up to 60% central) and pQCD+jet quenching

  17. partonic energy loss Is suppression an initial or final state effect? Initial state? Final state? gluon saturation How to discriminate? Turn off final state d+Au collisions

  18. Inclusive spectra RAB If Au+Au suppression is final state 1.1-1.5 1 If Au+Au suppression is initial state (KLM saturation: 0.75) ~2-4 GeV/c pT High pT hadron pairs broadening? pQCD: no suppression, small broadening due to Cronin effect saturation models: suppression due to mono-jet contribution? 0 suppression? /2  0  (radians) d+Au vs. p+p: Theoretical expectations All effects strongest in central d+Au collisions

  19. Inclusive yield relative to binary-scaled p+p • d+Au : enhancement • Au+Au: strong suppression • pT=4 GeV/c: • cent/minbias= 1.110.03 • central collisions enhanced wrt minbias Suppression of the inclusive yield in central Au+Au is a final-state effect

  20. pedestal and flow subtracted Azimuthal distributions Near-side: p+p, d+Au, Au+Au similar Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au Suppression of the back-to-back correlation in central Au+Au is a final-state effect

  21. STAR Preliminary v2(pT) : saturates? going down? NA45 - saturation at SPS? - RHIC: weak indication of decreasing..

  22. Have we found the Quark Gluon Plasma at RHIC? We now know that Au+Au collisions generate a medium that • is dense (pQCD theory: many times cold nuclear matter density) • is dissipative • exhibits strong collective behavior This represents significant progress in our understanding of strongly interacting matter We have yet to show that: • dissipation and collective behavior both occur at the partonic stage • the system is deconfined and thermalized • a transition occurs: can we turn the effects off ? Not yet, there is still work to do We have developed the tools necessary to complete this program

  23. pp Au+Au 40% to 80% STAR Preliminary STAR Preliminary 0 f0K0S  K*0 0 f0 K0S  K*0 0.2  pT  0.8 GeV/c 0.2  pT  0.9 GeV/c Things to Look Forward to This QM: First glance at resonances at RHIC: 0(770)  + - and f0(980)  + - |y| < 0.5 • Short-lived resonances: • provide information on the collision dynamics • rescattering  regeneration

  24. g conversion Single Electrons - Run I See talk R.Averbeck gconversion p0 gee h gee, 3p0 w ee, p0ee f ee, hee r ee h’  gee

  25. J/y e+e- in Gold-Gold ! N=10.8  3.2 (stat)  3.8 (sys) N=5.9 +  2.4 (stat)  0.7 (sys) N=10.8  3.2 (stat)  3.8 (sys) N=5.9 +  2.4 (stat)  0.7 (sys) Seven different mass fitting and counting methods used to determine systematic error in the number of counts.

  26. Our electron data is consistent with binary scaling within our current statistical and systematic errors. • NA50 has inferred a factor of ~3 charm enhancement at lower energy. We do not see this large effect at RHIC. • PHENIX observes a factor of ~3-4 suppression in high pTp0 relative to binary scaling. We do not see this large effect in the single electrons from charm. Possibly less energy loss of charm quarks in medium due to “dead-cone” effect.1 Observations NA50 - Eur. Phys. Jour. C14, 443 (2000). Binary Scaling PHENIX Preliminary Enhancement of Open Charm Yield N part 1Y.L.Dokshitzer and D.E. Kharzeev, hep-ph/0106202

  27. Warning This plot has been known to deceive theorists! Model Comparisons We show three different J/y patterns all normalized to intersect our proton-proton data point. (1) J/y scale with the number of binary collisions (2) J/y follow normal nuclear absorption with sJ-N=7.1 mb (3) J/y follow same pattern as NA50 (J/y / DY(mb))1 We show three different J/y patterns all normalized to intersect our proton-proton data point. (1) J/y scale with the number of binary collisions (2) J/y follow normal nuclear absorption with sJ-N=7.1 mb (3) J/y follow same pattern as NA50 (J/y / DY(mb))1 1NA50 Phys. Lett. B521, 195 (2001)

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