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Hadronic Probes of dense matter at RHIC From light to heavy flavors

Hadronic Probes of dense matter at RHIC From light to heavy flavors. Y. Akiba (RIKEN) DNP/JPS ’05 Kapalua, Hawaii, September 2005. The RHIC Experiments. RHIC. Probes of the evolution of the matter. pQCD direct photon Heavy quark production. q(x), g(x). Initial collision. Density

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Hadronic Probes of dense matter at RHIC From light to heavy flavors

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  1. Hadronic Probes of dense matter at RHICFrom light to heavy flavors Y. Akiba (RIKEN) DNP/JPS ’05 Kapalua, Hawaii, September 2005

  2. The RHIC Experiments RHIC

  3. Probes of the evolution of the matter pQCD direct photon Heavy quark production q(x), g(x) Initial collision Density Deconfined(?) Jet quenching /jet tomography Heavy quark energy loss J/Psi suppression Formation of dense matter EOS Viscocity tthermal Tini # of DOF Elliptic flow (Heavy quark) Elliptic flow (light hadron) Thermalization Quark number scaling of v2 Anomalous baryon J/Psi formation(?) time Hadronization Recombination(?) Chemical Freeze Out Hadron ratios Tchem mB Hadron spectra femotoscopy Tfo <bT> Thermal Freeze Out

  4. Topics covered by this talk Open heavy flavor Heavy quark production q(x), g(x) Initial collision Density Heavy quark energy loss Formation of dense matter EOS Viscocity tthermal Elliptic flow (Heavy quark) Elliptic flow (light hadron) Thermalization Quark number scaling of v2 Anomalous baryon time Hadronization Recombination(?) Chemical Freeze Out Hadron ratios Tchem mB Hadron spectra Tfo <bT> Thermal Freeze Out Light flavor hadrons

  5. Topics covered by the other speaker pQCD direct photon q(x), g(x) Initial collision Enegy density Deconfined(?) Jet quenching /jet tomography J/Psi suppression Formation of dense matter tthermal Tini # of DOF Thermal radiation Thermalization J/Psi formation(?) time Hadronization Recombination(?) Chemical Freeze Out They cover more initial stage of the evolution. The interest of the field is moving towards the study of partonic matter using penetrating probes Thermal Freeze Out

  6. Hadron spectra: Tfo and <bT> Heavy quark production q(x), g(x) Initial collision Enegy density Heavy quark energy loss Formation of dense matter EOS Viscocity tthermal Elliptic flow (Heavy quark) Elliptic flow (light hadron) Thermalization n-quark scaling of v2 Anomalous baryon time Hadronization Recombination(?) Hadron ratios Chemical Freeze Out Tchem mB Hadron spectra Tfo <bT> Thermal Freeze Out

  7. Hadron spectra – thermal freeze-out and radial flow • Hadron spectra are well reproduced by thermal distribution with radial expansion (blast wave model) • p/K/p spectra can be simultaneously fit with two parameters: Tfo: freezeout temp. bT: expansion velocity • Fit results Tfo ~ 110 MeV bT ~ 0.8 (<bT> ~ 0.6)

  8. RHIC Expansion velocity Tkin ~ 100 MeV <vT/c> ~ 0.4-0.6 Energy dependence of radial velocity • Blast wave model fits well hadron spectra data of A+A collisions from AGS to RHIC • The Fit results indicates that the expansion velocity increase with energy from <bT>~0.4 (AGS) to 0.6 (RHIC)

  9. W L X More data: strange baryon spectra 200 GeV Au+Au (STAR) 62.4 GeV Au+Au (STAR)

  10. Tch Thermal freeze-out of X, W • X, W : low hadronic cross section • They can freeze-out earlier Tfo of X, W is close to Tch. Still they have significant radial flow Another evidence for early development of flow(?)

  11. Particle ratios: Chemical equillibrium • Thermal model reproduces hadron ratios. • Tch ~ 160 MeV, mB ~ 30 MeV • Evidence for Chemical equillibrium

  12. BRAHMS PRELIMINARY Pbar/p vs K-/K+ in wide rapidity range BRAHMS In thermal model, pbar/p ratio measures baryon chemical potential mB The model descripbes pbar/p verus K-/K+ data well in wide rapidity range as well as the beam enery dependence with B= B(y) and T~170MeV  only B controls the particle ratio

  13. Elliptic flow Heavy quark production q(x), g(x) Initial collision Enegy density Heavy quark energy loss Formation of dense matter Elliptic flow (Heavy quark) Elliptic flow of light hadrons EOS Viscosity tthermal Thermalization n-quark scaling of v2 Anomalous baryon time Hadronization Recombination(?) Chemical Freeze Out Hadron ratios Tchem mB Hadron spectra Tfo <bT> Thermal Freeze Out

  14. Non-central Collisions z Reaction plane x y Reaction plane Elliptic Flow: Evidence for rapid thermalization • The matter produced at RHIC behaves like fluid. It “flows”. • The flow is strong evidence for rapid thermalisation of the matter. • Experimentally, the flow is measured as event anisotropy with respect to the reaction plane • The pattern of the “flow” is described by hydrodynamic calculation of ideal fluid (no viscosity) • Hydro-model needs very short thermalization time (t<0.6 fm/c) to reproduce the data. Large Pressure Collective Flow

  15. More elliptic flow data from RUN4 • More v2 data in • Wider Pt range • More identified hadrons • At Low pT, hydro-model reproduces v2 of heavy particles (f,L,X,W,etc) well • Strong Flow of multi-strange hadrons (small hadronic cross section) support that the flow develops at partonic stage

  16. Elliptic Flow is stronger at RHIC • Elliptic Flow is stronger in RHIC energy than in lower energies, and it is close to “hydrodynamic limit” of ideal fluid (no visocity)  Nearly perfect fluid Elliptic flow vs pT v2/ecc vs sqrt(s) PHENIX 200,62 GeV STAR (130GeV) PHENIX (62 GeV) PHENIX (200 GeV) NA49, CERES NA49

  17. v2/ecc and pT spectra proton pion But do all pictures fit together? Data vs Hydro-models comparison in PHENIX White Paper (NPA757(2005)184)

  18. A slide by T. Hirano (1WB6) Summary of Hydro Results “No-Go theorem” Ruled out! • WINNER for hydro race at RHIC ! • Hybrid model (Ideal QGP fluid + dissipative hadron gas) by Teaney, Lauret, and Shuryak

  19. Possible solution (by Hirano) • The agreement between ideal hydro-model and the data is due to “accidental cancellation of two effect: • Perfect fluidity of sQGP core (stronger v2) • Dissipative hadronic corona (reduce v2) • Caveat: • Detailed comparison between the hybrid model (3D hydro + hadron cascade) and the data is still forthcoming • If the hybrid model can reproduce all data (hadron spectra, hadron ratios, and v2), this will be a big step forward to an “unified model” of A+A collisons at RHIC • Will it also solve the long standing HBT puzzle?

  20. Hadronization and recombination Heavy quark production Initial collision q(x), g(x) Heavy quark energy loss Formation of dense matter Density EOS Viscocity tthermal Elliptic flow (Heavy quark) Elliptic flow (light hadron) Thermalization Quark number scaling of v2 Anomalous baryon time Hadronization Recombination(?) Chemical Freeze Out Hadron ratios Tchem mB Hadron spectra Tfo <bT> Thermal Freeze Out

  21. Anomalous p/p ratio Large p/p ratio in 2-4 GeV/c • A surprise: anomalous p/p ratio in intermediate pt (2 – 4 GeV/c) • The large p/p ratio can not be explained by usual fragmentation mechanism

  22. Recombination model • Recombination model explains the anomalous p/p ratio by a simple idea: • pT(baryon) ~ 3 * pT(q) • pT(meson) ~ 2 * pT(q) • For exponentially falling spectra, baryon is enhanced relative to meson • The model well repdoduces baryon/meson ratios in intermediate pT (2<pT<5 GeV/c)

  23. √sNN=200 GeV0-5% Au+Au/p+p STAR Preliminary Baryon vs meson; multi-strange baryon • behaves like proton, while f meson behaves like pion • The difference is due to baryon/meson, not due to the mass (Mf ~ Mp) • Support for recombination • Multi-strange baryon (X,W) show even stronger enhancement than L or p. • The enhancement increases with strangness • Can this be explained?

  24. Quark number scaling of v2(pT) • Complicated hadron species dependence of v2(pT) is observed • Recombination models explain the pattern by a simple quark number scaling: pT pT/n, v2 v2/n (meson: n=2, baryon: n=3)

  25. solid: STAR open: PHENIX PRL91(03) More particles added to the scaling plot • More data of v2 and RAA/RCP seem to support recombination picture. • But a few questions remain • Entropy conservation • Where are gluons? • Two particle correlation with leading baryon • Also: Can recombination model be accommodated into hydro+cascade model?

  26. Heavy quark: probes of early stage Heavy quark production Initial collision q(x), g(x) Density Energy loss mechanism Heavy quark energy loss Formation of dense matter Elliptic flow (Heavy quark) Elliptic flow (light hadron) thermalization Thermalization EOS Viscocity tthermal n-quark scaling of v2 Anomalous baryon time Hadronization Recombination(?) Chemical Freeze Out Hadron ratios Tchem mB Hadron spectra Tfo <bT> Thermal Freeze Out

  27. Measurement of open charm • Direct measurement of D meson: D0Kp, D+Kpp, D*Dp + Unambiguous signal - Small S/B (~1/600 in d+Au) • Limited statistics • Semi-leptonic method: De+X, m->X (BR~10%) + Large signal + High statistics • Background from light hadrons • Indirect measurement of D-meson kinematics • Can not distinguish b/c signal single lepton D e+X, m+X p+ DKp, DKpp

  28. D0 Signal by STAR d+Au at 200 GeV (RUN3) Au+Au at 200 GeV (RUN4) 6

  29. Open heavy quark measurement through leptons • open heavy quarks are measured by the semi-leptonic (electron) decay channel. • Lepton yield  total charm yield • Lepton pT specta  charm/beauty specta  Semi-leptonic decay channel g c e, medium s,d g

  30. PHENIX/STAR single lepton data • PHENIX e (|y|<0.35) and m (1.2<|y|<2.4) p+p  e, m @ 200 GeV d+Au  e, m @ 200 GeV Au+Au  e @ 200, 130 and 63 GeV • STAR e (|y|<1) by TPC(dE/dx)+TOF,EMCAL p+p  e @ 200 GeV d+Au  e @ 200 GeV Au+Au  e @ 200 GeV

  31. Single lepton in p+p by PHENIX PHENIX p+p at 200 GeV e : y = 0 nucl-ex/508034 m : y = -1.65 preliminary Cross sections of e and m are consistent

  32. STAR data in p+p, d+Au • Measured D-meson and single electron from charm in the same experiment. • The cross section is consistent within uncertainties. PRL94,062301

  33. Au+Au: Binary Scaling of Electron Yield • dN/dy of “Non-photonic” electrons for pT > 0.8 GeV/c scales with Ncoll • dN/dy ~ Ncolla where 0.906 < a < 1.042 within 90% C.L. • scc = Ncc/TAA= 622 ±57 (stat) ± 160 (sys) mb • Little nuclear modification of G(x), consistent with direct photon data. PHENIX PRL94 082301 (2005)

  34. Au+Au: higher statistics electron data from RUN4 • A surprise. Electrons from Heavy quark decay are suppressed at high pT! • Non-photonic =Inclusive - Cocktail • Curves: Binary scaled p+p reference • Significant improvement compared to Run02 analysis • Clear high pT suppression developing towards central collisions

  35. Nuclear Modification Factor RAA

  36. Large energy loss  Challenge to theory Single electron data indicates that heavy quark (charm) suffers substantial energy loss in the matter The large suppression requires a very large parton density or large c-quark-medium cross section: a challenge to the energy loss models Even b-quark is suppressed? q_hat = 0 GeV2/fm dNg / dy = 1000 (b+c) dNg / dy = 1000 (c) q_hat = 4 GeV2/fm (c) dNg / dy = 3500 (c) q_hat = 14 GeV2/fm (c)

  37. R_AA of non-photonic electron PHENIX STAR Both experiments reports significant suppression at high pT. However, the p+p reference is different, and the invariant yield in Au+Au is also different by a factor ~2. The difference need to be resolved for comparison with data.

  38. Greco,Ko,Rapp: PLB595(2004)202 V2 of electron from Heavy quark decay • V2(pT) of electron from heavy quark decay after subtracting photonic background. • Data clearly shows substaintial v2 of electrons • v2 of D-mesons Data at low pT favors models that charm quark itself flows • Even heavy quark flows in the matter PHENIX Preliminary

  39. v2(D)=v2(p) v2(D)=0.6 v2(p) v2(D)=0.3 v2(p) The matter is so strongly coupled that even heavy quarks flow • A simple model of D-meson v2 function form (v2(D) = a*v2(p) is used to evaluate the strength of D-meson v2 from electron data. • The comparison favors v2(D) ~ 0.6 * v2(p) • Charm flows, but not as strong as light mesons. • Drop of the flow strength at high pT. This can be due to b-quark contribution.

  40. Comparison of PHENIX and STAR data STAR reported a very large v2(e) in pT= 2-5 GeV/c in QM05. PHENIX and STAR data does not agree. The difference needed to be resolved Not shown were "30-40%" systematic errors.

  41. Comparison with models AMPT s=10mb R. Rapp (reso) AMPT s= 3 mb The large single electron v2 requires resonances (Rapp) or large c-matter cross section (AMTP) The different results in high pT (pT>2 GeV) from the two experiments should be resolved.

  42. Summary (1) • Light hadron data provide strong evidence for • Thermalized, expanding final state with Tfo~100 MeV and <bT>~0.6 (hadron spectra) • Chemical equilibrium among hadrons with Tch~170 MeV and mB~30 MeV (hadron ratios) • Rapid thermalization (t<0.6 fm/c) and ideal hydro-dynamical evolution (Elliptic flow) • Recombination model provides simple explanation of • anomolous (anti-)baryon/pion ratio • Quark number scaling of v2 • Challenge to theorists: • An unified description of all of the data is still absent. Can hybrid model of 3D hydro+hadron cascade be the solution?

  43. Summary (2) • New preliminary data on single electron from heavy quark decay bring two surprises • Large suppression at high pT: RAA~0.3-0.4 • Large elliptic flow: v2(e) ~ 0.1 @ 1.5-2 GeV/c • Charm energy loss and flow is strong evidence for very high density of the matter and rapid thermalization • Challenge to the theorists: • The data requires very strong interaction between matter and charm quark and very high parton density of the matter • Energy loss mechanism needed to be re-considered? • Challenges to experiments: • Publish the final results of the data • PHENIX/STAR difference need to be resolved

  44. Thank you for your attention

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