Empirical Constraints on Hadronization of Bulk Matter at RHIC

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 • Formation of Dense Matter in • Nucleus-Nucleus Collisions at RHIC • 2) Conventional Fragmentation Scheme Fails • 3) Nuclear Modification Factors RAA/RCP • and Azimuthal Angular Anisotropy v2 • 4) Features of RCP and v2 for Particle • Production at Intermediate pT • 5) Emerging Physical Scenario and Future • Experimental Verification

3. Formation of High Energy Density Matter • Experimental Evidences • 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 pT 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 pT 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. Coupling Strength q q Shorter distance  q q q q (GeV) Momentum Transfer 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 Quark pairs can be produced from vacuum No free quark can be observed

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

7. Too Many Baryons at Intermediate pT

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

9. Number of Participants Impact Parameter Geometry of Nucleus-Nucleus Collisions Npart – No of participant nucleons Nbinary – 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  RAA or RCP = 1 simple superposition of independent nucleon-nucleon collisions !

11. Particle Dependence of RCP suppression

12. coordinate-space-anisotropy  momentum-space-anisotropy y py px x Initial/final conditions, dof, EOS Elliptic Flow Parameter v2

13. STAR PHENIX Particle Dependence of v2 Baryon Meson Why saturation at intermediate pT ? Why baryon and meson difference ?

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

15. Salient Features at Inermediate pT • Why so many baryons versus mesons? • Why does elliptic v2 versus pT saturate ? • Why Rcp and v2 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 Hadronization Scheme for Bulk Partonic Matter: • KS – two quark coalescence • – three quark coalescence from the partonic matter surface?! Particle v2 may be related to quark matter anisotropy !! pT < 1 GeV/c may be affected by hydrodynamic flow ! 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. Volcanic mediate pT – Spatter (clumps) Quark Cluster Formation from Strongly Interacting Partonic Matter L X W 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 (RAA/RCP and v2)  all constituent quarks are almost equally important in determining particle properties ! v2 of hadron comes from v2 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 • Quantitative Energy Loss of light/heavy Quarks • Where does the Energy Loss Go? • Strange and Charm Quark Dynamics from Bulk Matter • Fluctuations, Phase Transition and Critical Point • 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 (Tinit > 500 MeV)! An Intriguing Scenario ?! RAA 1.0 Open Charm Require direct open charm measurement ! Light hadrons PT (pT scale)

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

22. A Critical Test for Recombination And Strange Quark Dynamics in Bulk Matter W f pT Scale !! STAR will make a measurement of W and f v2 from run-4 Au+Au data ! Duke Group, PLB 587, 73 (2004)

23. Recombination  DS/D0 PYTHIA Prediction Charm quark recombines with a light (u,d,s) quark from a strangeness equilibrated partonic matter  DS/D0 ~ 0.4-0.5 at intermediate pT !!!

24. pT Scales and Physical Processes RCP Three PT 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. Potential exotic particles/phenomena: penta-quark states (uudds, uudds!) di-baryons H – (L-L, uuddss) [W-W] (ssssss) strange quark matter meta-stable Parity/CP odd vacuum bubbles disoriented chiral condensate …… Discoveries from Unexpected Areas?! RHIC -- Frontier for bulk partonic matter formation (quark clustering and rapid hadronization) -- Factory for exotic particles/phenomena

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 pT particles the initial parton is considerably harder than if only one high pT particle is produced. Fragmentation region pT > 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: Deconfinement High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang High Baryon Density -- low energy heavy ion collisions -- neutron starquark star

30. Global Observables PRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03) 200 GeV 130 GeV PHOBOS 19.6 GeV Pseudo-rapidity Within |h|<0.5 the total transverse momentum created is 1.5x650x0.508 ~ 500 GeV from an initial transverse overlap area of pR2 ~ 153 fm2 ! hminus: Central Au+Au <pT>=0.508GeV/c pp: 0.390GeV/c Energy density e ~ 5-30 e0 at early time t=0.2-1 fm/c !

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

32. Charm and Bulk Matter Thermalization of partonic matter -- charm elliptic flow v2 ! -- charm hadron chemistry ! Does Charm Flow? Simulation by X. Dong Charm Meson v2 has to come from light quark v2 and possibly charm quark v2 !

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 pT particles the initial parton is considerably harder than if only one high pT particle is produced. Fragmentation region pT > 5.5 GeV/c 3) low level two particle correlations in the soft region can be accommodated in recombination/coalescence (wave induced correlation?)