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Heavy Quark Probes of Hadronization of Bulk Matter at RHIC

Heavy Quark Probes of Hadronization of Bulk Matter at RHIC. Huan Zhong Huang Department of Physics and Astronomy University of California at Los Angeles Department of Engineering Physics Tsinghua University. Collisions at high p T (pQCD).

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Heavy Quark Probes of Hadronization of Bulk Matter at RHIC

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  1. Heavy Quark Probes of Hadronization of Bulk Matter at RHIC Huan Zhong Huang Department of Physics and Astronomy University of California at Los Angeles Department of Engineering Physics Tsinghua University

  2. Collisions at high pT (pQCD) At sufficiently large transverse momentum, let us consider the process: p + p hadron + x • 1) f(x,m2) – parton structure function • 2) sab->cd – pQCD calculable at large m2 • 3) D(zh,m2) – Fragmentation function To produce heavy quark pairs, the CM energy must>2m

  3. l Heavy Quark Production Mechanism K+ e-/- e-/- e+/+ J/y K- e+/+ l D0 • Sensitive to initial gluon density and gluon distribution • Sensitive to initial gluon density and gluon distribution • Energy loss when propagating through dense medium • Suppression or enhancement of charmonium in the medium is a critical signal for QGP. • Different scaling properties in central and forward region indicate shadowing, which can be due to CGC.

  4. Parton Distribution Function Important

  5. Uncertainties in gluon structure function of the proton J. Pumplin et al, JHEP07(2002)012 MRST2001 CTEQ5M1 CTEQ5HJ Band – experimental constraints x

  6. Fragmentation Functions

  7. Fragmentation Functions from e+e Collisions Belle Data

  8. Charm Mesons from Hadronic Collisions Charm meson pT ~ follow the NLO charm quark pT -- add kT kick -- harder fragmentation (d func or recombination scheme)

  9. kT Kick? What about kL? The xF distribution matches the NLO charm quark xF !

  10. s(e+e-J/y cc) +0.15 + 0.12 = 0.59 - - 0.13 s(e+e-J/y X) Belle Puzzle ! PRL 89, 142001 (2002) An order of magnitude higher than theoretical predictions -- B.L. Ioffe and D.E. Kharzeev, PRD 69, 014016 (2004) These results challenge our current understanding of how charm quarks/mesons are produced. We may question our view for the underlying charm production process, e.g., the universality of fragmentation process and the fragmentation schemes !

  11. Neutral D mesons K ~ 1.5 LO QCD does not reproduce the cross sections ! K Factor !!

  12. K factor energy, particle dependent ! Charm-Beauty different ! We don’t know the production mechanism at all ! Charged D mesons K ~ 4.5

  13. Detecting D-Mesons via Hadronic Decays • Hadronic Channels: • D0  K(B.R.: 3.8%) • D0  K p r(B.R.: 6.2%  100% (rp+p-) = 6.2%) • D K p(B.R.: 9.1%) • D*±D0π (B.R.: 68%  3.8% (D0  K) = 2.6%) • Lc p K p (B.R.: 5%)

  14. General Techniques for D Reconstruction • Identify charged daughter tracks through energy loss in TPC • Alternatively at high pT use h and assign referring mass (depends on analysis) • Produce invariant mass spectrum in same event • Obtain background spectrum via mixed event • Subtract background and get D spectrum • Often residual background to be eliminated by fit in region around the resonance D0 D* D0 Exception D*: search for peak around m(D*)-m(D0) =0.1467 GeV/c2

  15. Detecting Charm/Beauty via Semileptonic D/B Decays • Semileptonic Channels: • D0  e+ + anything(B.R.: 6.87%) • D e + anything(B.R.: 17.2%) • B e + anything(B.R.: 10.2%)  single “non-photonic” electron continuum • “Photonic” Single Electron Background: • g conversions (p0 gg) • p0, h Dalitz decays • r, f, … decays (small) • Ke3 decays (small)

  16. TOF electron measurements 2/ndf = 65/46 2/ndf = 67/70 Electrons can be separated from pions. But the dEdx resolution is worse than d+Au Log10(dEdx/dEdxBichsel) distribution is Gaussian. 0.3<pT<4.0 GeV/c |1/-1|<0.03 2 Gauss can not describe the shoulder shape well. • Exponential + Gaussian fit is used at lower pT region. • 3 Gaussian fit is used at higher pT region.

  17. Dominant source at low pT Mass(e+e-)<0.15 GeV/c2 Electron Spectrum γ conversion π0Dalitz decay η Dalitz decay Kaon decay vector meson decays • Combinatorial background reconstructed by track rotating technique. • Invariant mass < 0.15 for photonic background.

  18. Charm pT Spectra D0 and e combined fit Power-law function with parameters dN/dy, <pT> and n to describe the D0 spectrum Generate D0e decay kinematics according to the above parameters Vary (dN/dy, <pT>, n) to get the min. 2 by comparing power-law to D0 data and the decayed e shape to e data <pT>=1.20  0.05(stat.) GeV/c in minbias Au+Au <pT>=1.32  0.08(stat.) GeV/c in d+Au

  19. Charm Total Cross Section Charm total cross section per NN interaction 1.13  0.09(stat.)  0.42(sys.) mb in 200GeV minbias Au+Au collsions 1.4  0.2(stat.)  0.4(sys.) mb in 200GeV minbias d+Au collisions Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors Indication of charm production in initial collisions Systematic error too large !

  20. Experimental Statistical and Systematic Errors c-cbar production CS PHENIX 0.92+-0.15+-0.54 mb STAR 1.4+-0.2+-0.4 mb Errors taken seriously High pT region does not contribute to total CS much. STAR data need to be compared with PHENIX data!

  21. Heavy Quarks Unique Heavy Quark Flavors (Charm or Beauty) Heavy Flavors once produced – do not change to light flavor easily heavy quark production can be calculated from pQCD approach more reliably than light quarks Trace heavy quark flavors in nuclear collisions -- collision dynamics and hadronization mechanism Fragmentation versus Recombination/Coalescence Fragmentation p(heavy quark meson)/p(heavy quark) < 1 Recombination/Coalescence p(heavy quark meson)/p(heavy quark) >= 1

  22. 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 !

  23. Charm and Non-photonic Electron Spectra 1.13  0.09(stat.)  0.42(sys.) mb in 200GeV minbias Au+Au collsions Total charm  Binary Scaling suppression at high pT

  24. Charm Nuclear Modification Factor RAA suppression for single electron in central Au+Au similar to charged hadrons at 1.5<pT<3.5 GeV/c Heavy flavor production IS also modified by the hot and dense medium in central Au+Au collisions at RHIC Suppressions!! STAR: Phys. Rev. Lett. 91 (2003) 172302

  25. electrons hadrons d K p p electrons High pT Electron ID dE/dx from TPC SMD from EMC

  26. electrons hadrons High pT Electron ID p/E from EMC After all the cuts

  27. The shape and yield at high pT Note: FONLL – effective fragmentation function harder than commonly used Peterson function! STAR – difference ~ 5.5 PHENIX -- ~1.7 (?)

  28. Non-photonic electron RAA Non-photonic electrons RAA -- similar magnitude as light hadrons -- STAR-PHENIX data consistent in the overlapping region The high pT region n-p electron RAA surprising !

  29. Heavy quark has less dE/dx due to suppression of small angle gluon radiation Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 “Dead Cone” effect M. Djordjevic, et. al. PRL 94(2005)112301 J. Adams et. al, PRL 91(2003)072304 Heavy quark energy loss: Early Expectations Radiative energy loss of heavy quarks and light quarks --- Probe the medium property ! What went wrong?

  30. Radiative Energy Loss not Enough Moore & Teaney, PRC 71, 064904 (2005) Large collisional (not radiative) interactions also produce large suppression and v2

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

  32. Does Charm Quark Flow Too ? Reduce Experimental Uncertainties !! Suppression in RAA Non-zero azimuthal anisotropy v2 !

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

  34. B D Poor (Wo)Man’s Approach to Measure B/D Contributions to Electrons – e-h correlations PYTHIA Simulations of e-h correlations from p+p X. Lin hep-ph/0602067

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

  36. Open Issues Phenix and STAR results  Converge?! Systematic errors on non-photonic electrons under control ! Quantitative description for energy loss and pT spectra for light/heavy quarks Collectivity for heavy quarks?

  37. 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 !!!

  38. HG Color Screening • J/ • Small: r ~ 0.2 fm • Tightly bound: Eb ~ 640 MeV QGP • Observed in dileptons invariant mass spectrum • Other charmonia • ’~ 8% •  ~ 32%

  39. 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/y. Charm quarks c-c may not bind Into J/y in high T QCD medium c c The J/y yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050) J/psi Suppression and Color Screening Recent LQCD Calculation:

  40. J/y Quark Potential Model

  41. Lattice QCD Calculations

  42. J/y from di-lepton Measurements J/- PHENIX Data Branching ratios: e+e- 5.93%; m+m- 5.88%

  43. J/psi is suppressed in central Au+Au Collisions ! Factor ~ 3 the same as that at SPS Satz: Only c states are screened both at RHIC and SPS. Alternative: Larger suppression in J/psi at RHIC due to higher gluon density, but recombination boosts the yield up !

  44. V2 of J/psi V2 of J/psi can differentiate scenarios ! pQCD direct J/psi should have no v2 ! Recombination J/psi can lead to non-zero v2 !

  45. The case for partonic DOF/Deconfinement can be made with strange vector meson f cannot be made from KK coalescence !

  46. J/y Suppression or Not Nuclear Absorption of J/y important at low energy important (SPS) ! Both QCD color screening and charm quark coalescence are interesting, which one is more important at RHIC? At RHIC the J/y measurement requires high luminosity running! Centrality and pT dependence important !

  47. 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? ) Where does heavy quark fit?

  48. The End

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