1. Empirical Constraints on Hadronization of Bulk Matter at RHIC International Workshop on QCD and Experiments at RHIC August 9-14, 2004 Beijing, P.R. China Huan Zhong Huang University of California at Los Angeles

2. Outline 1) Formation of Dense Matter in Nucleus-Nucleus Collisions at RHIC 2) Conventional Fragmentation Scheme Fails 3) Nuclear Modification Factors R AA /R CP and Azimuthal Angular Anisotropy v 2 4) Features of R CP and v 2 for Particle Production at Intermediate p T 5) Emerging Physical Scenario and Future Experimental Verification

3. Formation of High Energy Density Matter Experimental Evidences 1)Suppression of high transverse momentum particles and disappearance of back-to-back angular correlations  energy loss while traversing the dense medium  the energy loss also contributing to the production of soft particles correlated with the high p T particle -- Fuqiang Wang’s talk 2) Hydrodynamic features in particle production and azimuthal angular distributions  high energy density in initial conditions !

4. Why Not QGP Yet? High p T Phenomena – not directly sensitive to deconfinement though consistent with partonic state Hydrodynamical Behavior – not consistent with parton transport picture, failed to describe the space-time correlation (HBT) hadronization scheme dependent Confinement Signature ?

5. Salient Feature of Strong Interaction Asymptotic Freedom: Quark Confinement: 庄子天下篇 ~ 300 B.C. 一尺之棰，日取其半，万世不竭 Take half from a foot long stick each day, You will never exhaust it in million years. QCD qq qq q q Quark pairs can be produced from vacuum No free quark can be observed Momentum Transfer Coupling Strength Shorter distance  (GeV)

6. The Field & Feynman picture of cascade fragmentation Kretzer@ISMD04

7. Too Many Baryons at Intermediate p T

8. Baryon Production from pQCD  K K p p  e + e -  jet fragmentation from SLD Normal Fragmentation Cannot Produce the Large Baryon Yield

9. Geometry of Nucleus-Nucleus Collisions N part – No of participant nucleons N binary – No of binary nucleon-nucleon collisions cannot be directly measured at RHIC estimated from Woods-Saxon geometry

10. Nuclear Modification Factors Use number of binary nucleon-nucleon collisions to gauge the colliding parton flux: N-binary Scaling  R AA or R CP = 1 simple superposition of independent nucleon-nucleon collisions !

11. Particle Dependence of R CP suppression

12. Elliptic Flow Parameter v 2 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Initial/final conditions, dof, EOS

13. STAR PHENIX Particle Dependence of v 2 Baryon Meson Why saturation at intermediate p T ? Why baryon and meson difference ?

14. Strange quark dynamics are not significantly different from light quarks STAR Preliminary

15. Salient Features at Inermediate p T 1)Why so many baryons versus mesons? 2)Why does elliptic v 2 versus p T saturate ? 3)Why R cp and v 2 in two groups: Baryon and Meson ? 4)Why strange quark similar to light u/d quarks ? Hadronization from bulk partonic matter – Constituent quark degrees of freedom Recombination/Coalescence scheme for hadron formation Surface emission

16. Constituent Quark Degree of Freedom K S – two quark coalescence  – three quark coalescence from the partonic matter surface?! Particle v 2 may be related to quark matter anisotropy !! p T < 1 GeV/c may be affected by hydrodynamic flow ! Hadronization Scheme for Bulk Partonic Matter: Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Rafelski+Danos, Molnar+Voloshin …..) Quark Recombination – (R.J. Fries et al, R. Hwa et al)

17. Quark Cluster Formation from Strongly Interacting Partonic Matter Volcanic mediate p T – Spatter (clumps)   Strangeness enhancement from QGP is most prominent in the region where particle formation from quark coalescence is dominant !

18. Multi-Parton Dynamics for Bulk Matter Hadronization Essential difference: Traditional fragmentation  particle properties mostly determined by the leading quark ! Emerging picture from RHIC data (R AA /R CP and v 2 )  all constituent quarks are almost equally important in determining particle properties ! v 2 of hadron comes from v 2 of all constituent quarks ! Are constituent quarks the effective degrees of freedom for bulk partonic matter hadronization ? How do we establish signatures for multi-parton dynamics, recombination model for example, where thermal constituent quarks or shower partons from jet production are both possible ?

19. Future Measurements of QCD Properties of Bulk Matter 1)Quantitative Energy Loss of light/heavy Quarks 2)Where does the Energy Loss Go? 3)Strange and Charm Quark Dynamics from Bulk Matter 4)Fluctuations, Phase Transition and Critical Point 5)Initial Temperature of the Partonic System and Incoming Gluon Flux

20. Heavy Quark in QCD Medium Heavy Quark energy loss in color medium ! -- dead cone effect (less than light quarks) Charm enhancement from high temperature gluonic matter (T init > 500 MeV)! An Intriguing Scenario ?! PTPT R AA 1.0 Light hadrons Open Charm (p T scale) Require direct open charm measurement !

21. Energy Loss and Soft Particle Production Leading hadrons Medium STAR PRELIMINARY Fuqiang Wang’s work

22. A Critical Test for Recombination Duke Group, PLB 587, 73 (2004) p T Scale !!   And Strange Quark Dynamics in Bulk Matter STAR will make a measurement of  and  v 2 from run-4 Au+Au data !

23. Recombination  D S /D 0 PYTHIA Prediction Charm quark recombines with a light (u,d,s) quark from a strangeness equilibrated partonic matter  D S /D 0 ~ 0.4-0.5 at intermediate p T !!!

24. p T Scales and Physical Processes R CP Three P T Regions: -- Fragmentation -- multi-parton dynamics (recombination or coalescence or …) -- Hydrodynamics (constituent quarks ? parton dynamics from gluons to constituent quarks? )

25. Summary Formation of Dense Matter Partonic Degrees of Freedom Important Hadronization of Bulk Partonic Matter If So, the Dense Matter Must Be Deconfined Is It QGP?

26. Discoveries from Unexpected Areas?! RHIC -- Frontier for bulk partonic matter formation (quark clustering and rapid hadronization) -- Factory for exotic particles/phenomena Potential exotic particles/phenomena: penta-quark states (uudds, uudds!) di-baryons H – ( , uuddss) [  ] (ssssss) strange quark matter meta-stable Parity/CP odd vacuum bubbles disoriented chiral condensate ……

27. The End

28. Two Particle Jet-like Correlations Jet-like two particle correlations (e.g., trigger particle 4-6 GeV/c, associated particle 2-4 GeV/c) : These correlations cannot be easily explained in terms of recombination/coalescence scenario ! But 1) the effect of resonances on the two particle correlations has not be adequately addressed 2) trigger biases – with two high p T particles the initial parton is considerably harder than if only one high p T particle is produced. Fragmentation region p T > 5.5 GeV/c 3) low level two particle correlations in the soft region can be accommodated in recombination/coalescence (wave induced correlation?)

29. The Melting of Quarks and Gluons -- Quark-Gluon Plasma -- Matter Compression:Vacuum Heating: High Baryon Density -- low energy heavy ion collisions -- neutron star  quark star High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang Deconfinement

30. Global Observables PRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03) PHOBOS hminus: Central Au+Au =0.508GeV/c pp: 0.390GeV/c Pseudo-rapidity Within |  |<0.5 the total transverse momentum created is 1.5x650x0.508 ~ 500 GeV from an initial transverse overlap area of  R 2 ~ 153 fm 2 ! Energy density  ~ 5-30  0 at early time  =0.2-1 fm/c ! 19.6 GeV 130 GeV 200 GeV

31. Hydrodynamics Work at Low p T Thermostatistical model also describe the particle ratios well ! -- Another indication for constituent quark degrees of freedom?

32. Charm and Bulk Matter Does Charm Flow? Thermalization of partonic matter -- charm elliptic flow v 2 ! -- charm hadron chemistry ! Simulation by X. Dong Charm Meson v 2 has to come from light quark v 2 and possibly charm quark v 2 !

33. Recombination and Two-particle Jet-like Correlation Jet-like two particle correlations (e.g., trigger particle 4-6 GeV/c, associated particle 2-4 GeV/c) : These correlations cannot be easily explained in terms of recombination/coalescence scenario ! But 1) the effect of resonances on the two particle correlations has not be adequately addressed 2) trigger biases – with two high p T particles the initial parton is considerably harder than if only one high p T particle is produced. Fragmentation region p T > 5.5 GeV/c 3) low level two particle correlations in the soft region can be accommodated in recombination/coalescence (wave induced correlation?)