1 Evidence for Multi-parton Dynamics in Hadronization of Bulk Partonic Matter at RHIC Huan Zhong Huang ( 黄焕中 ) Department of Physics and Astronomy University of California Los Angeles Department of Engineering Physics Tsinghua University 7 th Annual Conference of Chinese High Energy Physics Society

2 Outline Relativistic Heavy Ion Collider (RHIC) and Quark-Gluon Plasma (QGP) Fragmentation Scheme Hadronization of Bulk Partonic Matter Recent Results of High p T Probes Outlook

3 STAR Relativistic Heavy Ion Collider --- RHIC Au+Au 200 GeV N-N CM energy Polarized p+p up to 500 GeV CM energy

4 Quark-Hadron Phase Transition

5 Au + Au Collisions at RHICSTAR Central Event (real-time Level 3)

6 Nucleus-Nucleus Collisions and Volcanic Eruption Volcanic high p T -- Strombolian eruption Volcanic mediate p T – Spatter (clumps) Volcanic low p T – Bulk matter flows

7 The Field & Feynman picture of cascade fragmentation

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

9 Too Many Baryons at Intermediate p T

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

11 Elliptic Flow: ultra-cold Fermi-Gas Li-atoms released from an optical trap exhibit elliptic flow analogous to what is observed in ultra- relativistic heavy-ion collisions  Elliptic flow is a general feature of strongly interacting systems!

12 Hydro calculations break-down at higher p T (as expected). How is v 2 established at p T above 2 GeV/c? Why is baryon v 2 larger than meson v 2 ? PRL 92 (2004) ; PRL 91 (2003) Elliptic Flow v 2

13 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)

14 Constituent Quark Scaling Constituent (n) Quark Scaling -- Meson n=2 and Baryon n=3 grouping Some deviation due to internal hadron structure

15 Nuclear Modification Factor N-binary Scaling  R AA or R CP = 1 simple superposition of independent N-N collisions !

16   Strangeness from Bulk Partonic Matter R CP  Constituent Quark Number Scaling -- Hadronization through quark clustering -- Effective DOF – constituent quarks quasi-hadrons at T c ? Lattice QCD picture? 

17 Intermediate p T Dynamics Multi-parton dynamics – clustering of quarks – could be responsible for -- increased baryon production -- strange baryon enhancement -- strong elliptic flow at intermediate p T !!! Hadronization of bulk partonic matter -- different phenomenon from e+e- collisions !

18 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? )

19 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 ! The fact that in order to explain the v 2 of hadrons individual constituent quarks (n=2-meson,3-baryon) must have a collective elliptic flow v 2 and the hadron v 2 is the sum of quark v 2  Strong Evidence for Deconfiement !

20 Recombination+Fragmentation Model basic assumptions: at low p t, the quarks and antiquark spectrum is thermal and they recombine into hadrons locally “at an instant”:  features of the parton spectrum are shifted to higher p t in the hadron spectrum at high p t, the parton spectrum is given by a pQCD power law, partons suffer jet energy loss and hadrons are formed via fragmentation of quarks and gluons shape of parton spectrum determines if recombination is more effective than fragmentation baryons are shifted to higher p t than mesons, for same quark distribution  understand behavior of baryons!

21 High p T Phenomena at RHIC Very dense matter has been created in central Au+Au collisions! This dense matter is responsible for the disappearance of back-to-back correlation and the suppression of high pT particles ! Is the energy loss due to parton or hadron stage? Is there a noticeable difference in experimental phenomenon related to quarks versus gluons?

22 The Suppression is the Same for   and  – parton level effect No suppression for direct photons – photons do not participant !

23 No Significant Difference Between Quarks and Gluons at High p T Baryons more likely from gluon fragmentations in the pQCD region

24 STAR No Significant Difference Between Heavy Quark Meson and Light Quark Mesons Non-photonic electrons from heavy quark decays Charged hadrons

25 Heavy quark energy loss: Early Expectations Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 Radiative energy loss of heavy quarks and light quarks --- Probe the medium property ! Heavy quark has less dE/dx due to suppression of small angle gluon radiation “Dead Cone” effect M. Djordjevic, et. al. PRL 94(2005) J. Adams et. al, PRL 91(2003) What went wrong?

26 B and D contributions to electrons Experimental measurement of B and D contributions to non-photonic electrons ! Direct measurement of D and B mesons

27 Poor (Wo)Man’s Approach to Measure B/D Contributions to Electrons – e-h correlations B D PYTHIA Simulations of e-h correlations from p+p X. Lin hep-ph/

28 STAR preliminary data motivated sonic-boom prediction F. Wang (STAR), QM’04 talk, nucl-ex/ Now published: STAR, PRL 95, (2005). p T trig =4-6 GeV/c, p T assoc = GeV/c Many recent studies: H. Stoecker, nucl-th/ Muller, Ruppert, nucl-th/ Chaudhuri, Heinz, nucl-th/ Y.G. Ma, et al. nucl-th/ Casalderrey-Solana, Shuryak, Teaney, hep-ph/ Actually sonic-boom was first predicted in the 70’s by the Frankfurt school.

29 High p T Phenomena at RHIC Very dense matter has been created in central Au+Au collisions! This dense matter is responsible for the disappearance of back-to-back correlation and the suppression of high pT particles ! The mechanism for parton energy loss is yet to be understood ! The nature for the broad peak on the away-side requires more studies (Mach cone or not) !

30 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 ……

31 STAR – Exciting Physics Program A full TOF upgrade will greatly enhance STAR’s capability !! RHIC – Exotic Particle Factory Full Barrel TOF Using MRPC Chinese STAR Group SINAP Tsinghua University USTC CCNU, Wuhan IMP, Lan Zhou IHEP Construction to be finished by 2008 Full installation in 2009

32 RHIC Physics Outlook Heavy Ion Physics: 1) Properties of high density QCD matter 2) Chiral symmetry at high temperature and density 3) Search for exotic particles/phenomena at RHIC 4) Search for critical point (low energy scan) RHIC Spin Physics Using Polarized p+p Collisions: 1) the gluon spin structure function  major milestone to understand the spin of the proton! 2) sea quark spin structure function 3) quark transverse spin distribution

33 End of Talk

34 Experimental Statistical and Systematic Errors c-cbar production CS PHENIX mb mb STAR mb Errors taken seriously High pT region does not contribute to total CS much. Difference between STAR and PHENIX has to be resolved !!

35 B does not seem dominant at pT 4.5 GeV/c Preliminary STAR Data Xiaoyan Lin – STAR presentation at Hard Probe 2006

36 Intriguing Situation Regarding Pentaquark States pK + and pK - from 18.4 M d+Au at 200 GeV Background – Combinatorial and Correlated Pairs Statistical significance ~ 4  Intriguing ! Not conclusive yet ! Another long d+Au run will resolve this uncertainty ! M (GeV/c 2 )  

37 Intermediate p T Region Volcanic mediate p T – Spatter (clumps) At RHIC intriguing experimental features: multi-quark clustering  enhanced baryon over meson production strangeness equilibration  increased multi-strange hypeons

38 Radiative Energy Loss not Enough Moore & Teaney, PRC 71, (2005) Large collisional (not radiative) interactions also produce large suppression and v 2

39 Charm Quark in Dynamical Model (AMPT) Large scattering cross sections needed !

40 Nuclear Modification Factor R AA R CP Multi-parton dynamics predict baryon yield increases with centrality FASTER than mesons! Yield ~  n and n  >n K  a feature not present in single parton fragmentation ! Multi-parton dynamics: coalescence, recombination and gluon junctions. R CP R CP = [yield/N-N] central [yield/N-N] peripheral

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

42 Spin Physics Program The Spin Structure of the Proton: ½ = ½   q +  G + q  up, down and strange quarks G  gluons L  angular momentum of quarks and gluons Experimentally: 1) total spin in quarks ~ 30% 2) sea quarks are polarized too 3) little info about the gluon polarization 4) even less know about and how to measure