1 Recent Results from RHIC Huan Zhong Huang 黄焕中 Department of Physics and Astronomy University of California Los Angeles Department of Engineering Physics Tsinghua University Mar 23,

2 Outline High p T and Heavy Quark Measurements Hadronization of Bulk Partonic Matter Outlook

3 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

4 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? What is the flavor dependence of energy loss? Particle emission pattern associated with E Loss?

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

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

7 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?

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

9 Does Charm Quark Flow Too ? Reduce Experimental Uncertainties !! Suppression in R AA  Non-zero azimuthal anisotropy v 2 !

10 B and D contributions compatible Bottom quarks may suffer considerable energy loss in the dense partonic medium too !

11 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.

12 R.B. Neufeld (preliminary) u = 0.75 c  (z - ut)  u = c Mach cone in QCD vs. N=4 SYM Chesler & Yaffe arXiv: Energy Density Energy Flux

13 In order to discriminate Mach-cone from deflected jets, one needs three-particle correlation. away near Medium mach cone Medium away near deflected jets  1  2   0 0  1  2  0 0 

14 Conic Emission in 3-hadron Correlations Au+Au 0-12% (  1 -  2 )/2 Au+Au 0-12%

15 Mach cone or Cerenkov gluons? Angle predictions: Mach-cone: Angle independent of associated p T Cerenkov gluon radiation: Angle decreases with associated p T STAR Preliminary Cone angle (radians) p T (GeV/c) (  1 -  2 )/2 Au+Au 0-12% Central Au+Au results consistent with Mach cone emission Naive calc. of time averaged velocity of sound in medium: Cone angle ~ 1.36 radians c s = 0.2c ??!

16 Reaction Plane Dependence 3<p T trig <4GeV/c & 1.0<p T asso <1.5GeV/c 20-60% STAR At low p T region, study the medium response to jets - Away side (medium side): single  double peaks - Near side (jet side): amplitude reduced  =  associate -  trigger (rad) STAR—Aogi Feng (CCNU)

17 Does Heavy Quark Energy Loss Generate Mach Cone Emission? Trigger on non-photonic electrons from heavy quark decays -- Preliminary STAR data show a broadening peak at the away side ! AWAY SIDE NEAR SIDE 200 GeV Cu+Cu Pythia result Gang Wang (UCLA)

18 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 ! There is a conic emission of particles when partons lose energy in medium, but the nature of the conic emission yet to be determined!

19 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

20 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)

21   Strangeness from Bulk Partonic Matter R CP  ss  Constituent Quark Number Scaling -- Hadronization through quark clustering -- Effective DOF – constituent quarks quasi-hadrons at T c ? Lattice QCD picture?  Jinhui Chen et al (SINAP)

22 STAR Preliminary p T (GeV/c) At intermediate p T  (sss) and  (ss) should be dominated by bulk thermal quark coalescence – no jet contribution (Hwa and Yang PRC 75, (2007)) It appears that thermal quark coalescences dominate the particle production below pT 4 GeV/c, for both central Au+Au and Cu+Cu collisions Xiaobin Wang (Tsinghua U.) --  Jinhui Chen (SINAP) --   and  production from coalescence

23 Parton P T Distributions at Hadronization If baryons of p T are mostly formed from coalescence of partons at p T /3 and mesons of p T are mostly formed from coalescence of partons at p T /2  and  particles have no decay feeddown contribution !  decay contribution is small These particles have small hadronic rescattering cross sections

24 Strange and down quark distributions s distribution harder than d distribution perhaps related to higher s quark mass in partonic evolution Independent Test –  /s should be consistent with s quark distribution Yes ! Jinhui Chen et al (SINAP/UCLA)

25 Test on s/d Quark Ratios s/d quark ratios =  =  yes! but with large uncertainties due to decay feeddown corrections in 

26 QCD Color Screening: (T. Matsui and H. Satz, Phys. Lett. B178, 416 (1986)) A color charge in a color medium is screened similar to Debye screening in QED  the melting of J/ . cc Charm quarks c-c may not bind Into J/  in high T QCD medium The J/  yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/ ) Debye Screening of Color Charge -- quarkonium melting in QGP J/  ’ and  c will melt in high temperature Quark-Gluon Plasma ! The melting temperatures for  ’ and  c are lower ! J/  may not melt until the temperature is higher than 2T c ?!

27 J/  is suppressed, but the physical mechanism is not clear ! The pT, rapidity and Npart dependence of J/  production cannot be explained yet! The suppression at forward rapidity seems to be larger than at mid-rapidity ! Note parton density should be higher at mid-rapidity.

28 Suppression + Regeneration Zhuang, Pengfei et al, Phys. Rev. Lett. 97:232301,2006

29 Two Component Approach: X. Zhao and R. Rapp, hep-ph/ J/  non-suppression at high pT Zebo Tang (USTC)

30 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 ! ---- Evidence for Deconfinement !!! Hadronization of bulk partonic matter -- different phenomenon from e+e- collisions ! J/  suppression and regeneration – More accurate experimental data and elliptic flow of J/  !

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 FY2008 Run – d+Au until mid-Feb 4 weeks of p+p

33 End of Talk

34 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

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

36 Constituent Quark Scaling STAR PHENIX Baryon Meson Constituent (n) Quark Scaling -- Meson n=2 and Baryon n=3 grouping Saturation of v 2 at Intermediate p T

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

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

39 s and d quark distributions physical AMPT model using string-melting and coalescence can fit v 2 but fails pT spec Using our s-d quark distribution AMPT can fit pT spec -- Early evolution important in determining quark distributions!

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

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