1 Strange and Heavy Quark Probes of QCD Matter at RHIC Huan Zhong Huang Department of Physics and Astronomy University of California Los Angeles Weihai, China 2004

2 Outline Relativistic Heavy Ion Collider (RHIC) and Quark-Gluon Plasma (QGP) Intriguing New Experimental Phenomena at RHIC Strange and Heavy Quarks at RHIC Future Measurements

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 The STAR Collaboration: 49 Institutions, ~ 500 People England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt India: Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC Netherlands: NIKHEF Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvino U.S. Labs: Argonne, Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan, USTC, Tsinghua, SINR, IMP Lanzhou Croatia: Zagreb University Czech Republic: Institute of Nuclear Physics

5 Quark-Hadron Phase Transition

6 New Phenomena at RHIC 1)High p T Particle Suppression and Disappearance of back-to-back Correlation 2)Saturation of Elliptic Flow v 2 3)Hydrodynamic Flow of Bulk Matter

7 Hard Scattering and Jet Quenching back-to-back jets disappear leading particle suppressed Hard Scattering in p+p Parton Energy Loss in A+A Reduction of high p T particles Disappearance of back-to-back high p T particle correlations

8 Disappearance of back-to-back correlation ! Disappearance of back-to-back angular correlations x y p trig p ss p os P trig – p ss same side  correlation P trig – p os opposite side  corr. p trig > 4 GeV/c, p ss p os 2<p T <p trig

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 Naïve Expectation for Au+Au 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 ! High p T particles are from hard scattering of partons --

11 Suppression of high p T particles p T Spectra Au+Au and p+p p+p Au+Au 0-5% R AA =(Au+Au)/[N binary x(p+p)] Strong high p T suppression by a factor of 4-5 in central Au+Au collisions ! The suppression sets in gradually from peripheral to central Au+Au collisions !

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

13 Saturation of Elliptic Flow v 2 v 2 saturation  related to geometry of the emission source v 2 non-zero at pT 5-6 GeV/c  particle production source not transparent to moderate p T particles

14 Hydrodynamics Works at RHIC Nucl-ex/ Ideal hydrodynamic fluid  the mean free path of the constituent partons ~ zero ! How?

15 High Density Matter at RHIC Experimental Evidences for High Density Matter: 1) High p T Suppression in Central Au+Au and Disappearance of back-to-back Correlations 2) Elliptic Flow v 2 Saturation at Intermediate p T 3) Hydrodynamic Limit for Bulk Particle Production Why not QGP yet? 1) not directly sensitive to deconfinement 2-3) not consistent with parton transport picture, failed to describe the space-time correlation (HBT) hadronization scheme dependent

16 Initial Energy Density Estimate PRL 85, 3100 (00); 91, (03); 88, (02), 91, (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

17 Strange and Heavy Quarks at RHIC Strangeness Equilibration ? Hadronization Scheme, in particular, for dense partonic matter ? Signature for a deconfined matter?

18 Particle Spectra

19 Strange Baryon Production from Au+Au 200 GeV

20 Strangeness Equilibration?

21 Nuclear Modification Factors Very distinct meson versus baryon dependence ! P T scale for fragmentation ~ 5 GeV/c or above !

22 Particle Dependence of v 2 STAR PHENIX Baryon Meson

23 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

24 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)

25 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 !

26 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 ?

27 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? )

28 Future Perspectives 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

29 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 !

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

31 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 !

32 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 ~ at intermediate p T !!!

33 Fragmentation vs Recombination Fragmentation Function  z = p hadron /p parton < 1 Recombination Scheme  p hadron = p parton-1 + p parton-2 …  Z >= 1

34 Fragmentation Functions from e+e Collisions Belle Data

35 Charm Mesons from Hadronic Collisions Charm meson p T ~ follow the NLO charm quark p T -- add k T kick -- harder fragmentation (  func or recombination scheme)

36 k T Kick? What about k L ? The x F distribution matches the NLO charm quark x F !

37 The RHIC D meson p T ~ NLO charm quark too NLO pQCD predictions are provided by R. Vogt, hep-ph/ STAR Preliminary But NLO QCD calculation fits CDF data within a factor of 2 Recombination mechanism for D formation ?!

38 B Quark Cross Section at RHIC The bottom quark production cross section at RHIC ?

39 Summary Formation of Dense Matter Partonic Degrees of Freedom Important Hadronization of Bulk Partonic Matter Is Recombination Scheme Necessary? If So, the Dense Matter Must Be Deconfined Is It QGP?

40 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 ……

41 The End

42 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?)

43 Charm and Bulk Matter Volcanic low p T – Bulk matter flows Does Charm Flow? Thermalization of partonic matter -- charm elliptic flow v 2 ! -- charm hadron chemistry !

44 Two Explanations for High p T Observations Energy Loss: Particles lose energy while traversing high density medium after the hard scattering. Energy loss quenches back-to-back angular correlations. J. Bjorken, M. Gyulassy, X-N Wang et al…. Parton Saturation: The parton (gluon) structure function in the relevant region (saturation scale) is modified. Not enough partons available to produce high pT particles. Parton fusion produces mono-jet with no back-to- back angular correlations. D. Kharzeev, L. McLerran, R. Venugopalan et al…..

45 RHIC Heavy Quark Physics Program RHIC Exp Program from PHENIX and STAR: Au+Au data on charm and beauty,Charm flow, J/  and Upsilon ! Detector Upgrade: PHENIX -- VTX STAR -- TOF and microVertex Detector (MVD) !

46 Charm and Beauty reflect QCD Properties of Matter Initial gluon flux and initial temperature of the gluon-dominated matter Transition temperature from partons to hadrons Color degree of freedom of the matter – definement Heavy Quark in the forward region -- CGC

47 Chemical Freeze-out Conditions Strangeness Enhancement Resonances STAR O PHENIX Central Au+Au data can be described by thermal statistical model with T ch = MeV and quark chemical potential ~ 8-10 MeV !

48 Kinetic Freeze-out Conditions Final flow = partonic + hadronic Some particles (  ) have less contributions from hadronic phase

49 d+Au Collisions q q q q Au+Au Geometry d+Au Geometry d+Au collisions: Little energy loss from the dense medium created, But Parton saturation from Au nuclei persists!

50 Data from d+Au collisions No high p T suppression ! No disappearance of back-to-back correlations!

51 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 !

52 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

53 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 !

54 Multi-Parton Dynamics K S – two quark coalescence  – three quark coalescence from the partonic matter surface?! V 2 /n versus p T /n indicates quark matter anisotropy !! 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….) STAR+PHENIX

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

56 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

57 Strangeness from Bulk Partonic Matter Strangeness enhancement is most prominent at intermediate p T from quark coalescence in an equilibrated bulk matter !   R CP

58 Low p T Phenomenon at RHIC Volcanic mediate p T – Spatter (clumps) Volcanic low p T – Bulk matter flows Prominent features at low p T : bulk matter flows ! 1) Thermal statistical models can describe the yield of most particles. 2) Particle p T spectra and elliptic flow v 2 – hydrodynamics.

59  = Infinite Nuclear Collision Evolution Epoches Chemical Freeze-out --- formation of hadrons Kinetic Freeze-out --- Interaction ceases

60 Dynamics between chemical and kinetic freeze-out Torrieri and Rafelski Phys. Lett. B509 (2001) 23. Particles form at the chemical freeze-out Resonances decay and daughters rescatter and disappear. Sensitive to time span between particle formation and kinetic freeze-out.

61 Between Two Epoches: Resonance Physics Au+Au 40% to 80% 1.2  p T  1.4 GeV/c |y|  0.5 STAR Preliminary K *0   *(1520) STAR preliminary p+p at 200 GeV , f 0,  *(892), , ,  *(1385),  *(1520) ρ 0 f 0 K 0 S ω K *0 f 2  0 & f 0  ++ p+p

62 Messenger for Conditions at Phase Boundary Particles with small hadronic rescattering cross sections can be used to probe phase boundary at the hadron formation: , , , D, J/  STAR Preliminary 

63 RHIC Physics Outlook Heavy Ion Physics: 1) discovering the Quark Gluon Plasma 2) Properties of high density QCD matter 3) Chiral symmetry at high temperature and density 4) Search for exotic particles/phenomena at RHIC 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

64 The UCLA Group Faculty: Huan Zhong Huang and Charles Whitten Staff: Stephen Trentalange and Vahe Ghazikhanian Research Associate: Oleg Tsai and An Tai Post-doc: Joanna Kiryluk and Hui Long Graduate Students: Jeff Wood, Dylan Thein, Steve Guertin, Jingguo Ma, Johan Gonzalez, Weijiang Dong and Hai Jiang Recent Ph.D. Graduates on STAR physics: Eugene Yamamoto (2001) Hui Long (2002) Yu Chen (2003) Paul Sorensen (2003)

65 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

66 RHIC Spin Physics At RHIC we use polarized p+p collisions to study 1)Gluon spin structure function q+g  q+  2)Sea quark spin structure function q+q  W boson 3)Quark transverse spin distribution Essential to measure photons, electrons and jets ! Electromagnetic Calorimeter: Lead/Plastic Scintillator sandwich, Shower Max Detector for electron/hadron separation. Major Detector Construction at Wayne State University and UCLA

67 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)

68 Kinetic Freeze-out Condition Hydrodynamics-inspired model fit  most particles decouple at T~ 100 MeV and expansion velocity ~ 0.55c ! Some particles decouple at earlier time because of smaller coupling strength with the hadronic medium! important messengers of partonic matter !

69 Building Blocks of Hadron World ProtonNeutron (uud)(uud)(udd)(udd) Mesons (q-q) Exotics (qqqq-q,…) Molecules Atoms Electrons Strong interaction is due to color charges and mediated by gluons. Gluons carry color charges too. Baryon Density:  = baryon number/volume normal nucleus  0 ~ 0.15 /fm 3 ~ 0.25x10 15 g/cm 3 Temperature, MeV ~ 1.16 x K second after the Big Bang T~200 MeV Nucleus Hyperons (s…)

70 What More Measurements ? Experimentally determine the amount of jet energy loss? Where did the energy loss go (increase in soft particle emissions?) Is the experimental energy loss consistent with theoretical calculation of dE/dx from a QCD medium, not with a hadronic medium? Signatures of QCD deconfinement? Peoperties of bulk partonic matter at the phase boundary? Practically we need Au+Au, Si+Si …… at several beam energies , , J/ , open charm mesons, direct photons…..

71 y Dynamical Origin of Elliptic Flow STAR Preliminary Au+Au 200 GeV V 2 in the high p T region: should large parton energy loss lead to surface emission pattern ?! Particle Dependence of v 2 ? Collective Pressure High pressure gradient Large expansion velocity Small expansion velocity p T dependent ! Surface Geometrical Phase Space Surface Emission Pattern High particle density Low particle density p T independent ! or p T dependence may come from surface thickness (p T ) x

72 Energy Scale and Phase Transition Entity Energy Dimension PhysicsBulk PropertyP/T Atom10’s eV mIonizatione/Ion PlasmaNo Nucleus 8 MeV mMultifrag.Liquid-GasY(?) QCD200 MeV mDeconfine.QGPY(?) EW100 GeV mP/CP Baryon AsymmetryY(?) GUT GeVSupersymmetry TOE10 19 GeVSuperstring

73 A Magnificent Collision in the Universe Collision of two galaxies: the Antennae; Hubble Space Telescope