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What did we learn at RHIC?

原子核・ハドロン物理：横断研究会. What did we learn at RHIC?. Tetsufumi Hirano Dept. of Physics The University of Tokyo. 「原子核・ハドロン物理： 横断 研究会」におけるレビュー講演  原子核の他分野の方々に当該分野の 現状を報告 ＳＰＩＲＥＳを使って引用数の多いＲＨＩＣ実験論文を理論屋（現象論屋）の立場から眺めてみよう。 良い点：限られた時間で（客観的に）重要なトピックスに絞れる 悪い点：最新の結果に触れられない （私個人として、）何が分かって、何を目指すべきか。.

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What did we learn at RHIC?

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  1. 原子核・ハドロン物理：横断研究会 What did we learn at RHIC? Tetsufumi Hirano Dept. of Physics The University of Tokyo

  2. 「原子核・ハドロン物理：横断研究会」におけるレビュー講演  原子核の他分野の方々に当該分野の現状を報告 ＳＰＩＲＥＳを使って引用数の多いＲＨＩＣ実験論文を理論屋（現象論屋）の立場から眺めてみよう。 良い点：限られた時間で（客観的に）重要なトピックスに絞れる 悪い点：最新の結果に触れられない （私個人として、）何が分かって、何を目指すべきか。 My Charge(?)

  3. What is RHIC? Relativistic Heavy Ion Collider(2000-) front view STAR side view STAR Purpose: Create a transient state of the QGP at high temperature and energy density in a laboratory and investigate its property.

  4. これまでのＲＵＮ 加速器側で制御できる のはせいぜい当てる原 子核とエネルギー • Size dependence • Energy dependence • Control experiment • (spin) 織田さん（ＣＮＳ）のトーク＠RCNP（‘０７）から

  5. FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007) カッコ内はそのうちTOPCITE 250+

  6. Dynamics of Heavy Ion Collisions Freezeout “Re-confinement” Expansion, cooling Thermalization First contact (two bunches of gluons) Time scale 10fm/c~10-23sec <<10-4(early universe) Temperature scale 100MeV~1012K

  7. y Ncoll & Npart Thickness function: x Gold nucleus: r0=0.17 fm-3 R=1.12A1/3-0.86A-1/3 d=0.54 fm Woods-Saxon nuclear density: # of binary collisions # of participants sin = 42mb @200GeV 1－（survival probability）

  8. Centrality （検出器側の制御） Au+Au 200 GeV • Npart and Ncoll as a function • of impact parameter • Categorize events with • Npart or Ncoll PHENIX: Correlation btw. BBC and ZDC signals

  9. FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007) カッコ内はそのうちTOPCITE 250+

  10. Centrality Dependence of Multiplicity PHOBOS,PRC65,061901(’02) Cited 105 times PHENIX, PRL86,3500(‘01) Cited 194 times • EKRT: final state saturation (Eskola et al.) • HIJING: event generator (string+jet) (Wang-Gyulassy) • Saturation Model: color glass condensate (Kharzeev-Levin) • Nch ~ 5000(700) in very central collisions (at midrapidity) • ~90% from soft particle production • Serves a severe test for models of particle production

  11. Energy Density Bjorken formula (’83) Volume of cylinder ec from lattice Sorry, I could not find the original paper. PHENIX, PRL87,052301(’01) Cited 121 times • Assuming t=1fm/c, well above ec from lattice in central collision at RHIC • Necessary condition to study the QGP at RHIC

  12. Particle Relative Yield STAR, PRL92,112301(’04) Cited 161 times STAR,NPA757,102(’05) Cited 408 times • Tch = 157 +- 6 MeV, mB = 22 +- 4 MeV • Really equilibrated in peripheral collisions? • Just fitting parameters?

  13. pT spectra Blast wave model (thermal+boost) PHENIX, PRC69,034909(’04) Cited 268 times • Blue-shifted spectra are evidence of radial flow • Blast wave model gives b = 0.48+-0.07 in 0-5% bin. • Quantitative interpretation needs dynamical model.

  14. FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007) カッコ内はそのうちTOPCITE 250+

  15. What is Elliptic Flow? J.Y.Ollitrault,PRD46,229 (’92) How does the system respond to spatial anisotropy? No secondary interaction Hydro behavior y f x INPUT Spatial Anisotropy 2v2 Interaction among produced particles dN/df dN/df OUTPUT Momentum Anisotropy 0 f 2p 0 f 2p

  16. Multiplicity Dependence of v2 Response = (output)/(input) P.F.Kolb et al.,PRC62,054909(’00) Particle Density • Experimental data reach • “hydrodynamic limit” • for the first time at RHIC • But, only one data point? STAR, NPA757,184(’05) Cited 410 times STAR, PRC66,034904(’02) Cited 162 times

  17. pT dependence of v2 PHENIX,PRL91,182301(’03) Cited 242 times STAR, PRC72,014904(’05) Cited 127 times Hydro calculations: P.Huovinen • A hydrodynamic model based on perfect fluids • reasonably describes pi, K, p, Lambda data • in low pT region. • How small is viscosity? • How fragile/robust?  See our recent papers

  18. Hydrodynamic Model Final stage: Free streaming particles  Need decoupling prescription t Intermediate stage: Solve energy-momentum conservation.  Need EoS and/or transport coefficients z 0 • Initial stage: • Particle production, • pre-thermalization, instability? • Instead, initial conditions for hydro simulations

  19. FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007) カッコ内はそのうちTOPCITE 250+

  20. Two-Particle Correlation Function C2 F Bertsch-Pratt equation • Inverse problem to get source information

  21. Bertsch-Pratt parameterization Bird’s eye view View from beam axis p1 Rside y KT q Rlong p2 Rout x reaction plane z l C2 Two-pion correlation function 1/R 1 q

  22. KT Dependence of HBT Radii PHENIX, NPA757,184(’05) Cited 410 times PHENIX, PRL88,192302(’02) Cited 128 times STAR, PRL87,082301(’01) Cited 193 times Hydro(-based) calculation Soff, Kolb,Hirano,… • Hydro models do not give correct source sizes. • HBT puzzle in a narrow sense • Last interaction point  Hydro description is not valid.

  23. FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007) カッコ内はそのうちTOPCITE 250+

  24. Tomography CT (computed tomography) scan • “Tomography” • Known probes: Spectra reliably calculable via pQCD • Good detector: RHIC experiments! • Interaction btw. probes and unknowns: • Recent development in this field *平野哲文、浜垣秀樹、「ジェットで探るクォークグルーオンプラズマ」、日本物理学会誌2004年12月号

  25. Jet Tomography Tool 1. Jet quenching Bjorken(’82) Gyulassy,Plümer Wang (’90) g g 180 deg. correlation? g High “density” matter Bjorken(’82) Appel (’86) Blaizot & McLerran (’86) Tool 2. Jet acoplanarity

  26. Nuclear Modification Factor • Au+Au 0-10% central • b=2.8 fm • Ncoll = 978 • Npart = 333 • Npart/Ncoll = 0.341 (null result) binarycollisionscaling 1 RAA participant scaling 0.341 pT

  27. High pT Spectrum in pp Collisions • NLO pQCD works at RHIC • Important for AA collisions • Serves a reference spectrum PHENIX, PRL91,241803(’03) Cited 193 times

  28. Nuclear Modification Factor charged PHENIX, PRL88,022301(‘02) Cited 402 times STAR, PRL89,202301(’02) Cited 292 times • RAA < 1 for the first time at RHIC • Significant suppression in central collisions

  29. Di-hadron Distribution 4<pT,trigger<6 GeV/c 2 GeV/c<pT,associate<pT,trigger ??? STAR, PRL90,082302(’03) Cited 341 times • Disappearance of away-side peaks in central collisions • Away side jet may be gone.

  30. Initial vs. Final I.Vitev and M.Gyulassy, PRL89, 252301(‘02) D.Kharzeev et al., PLB561, 93(‘03). • Saturation  Npart scaling • (Later, ∃Cronin peak even within CGC) • ggg (no back-to-back) • Jet quenching • dNg/dy =500-1200 @ RHIC Importance of pA (dAu) collisions

  31. Results from d-Au Collisions STAR,PRL91,072304(’03) Cited 314 times PHENIX, PRL91,072303(’03) Cited 276 times

  32. Results from d-Au Collisions BRAHMS, PRL91,072305(’05) Cited 204 times PHOBOS, PRL91,072302(’03) Cited 169 times • Neither suppression nor disappearance in d+Au • Jet quenching scenario turns out to be favored. • This does not mean saturation models • are killed.

  33. High pT at forward h=0 h=2.2 BRAHMS, PRL91,072305(’03) Cited 204 times • More suppression at forward, or initial state effect?

  34. Kinematic Effect Jet quenching Spectrum shift Ratio at a fixed pT. Different slope, but same shift “parallel shift” (1/pT)dN/dpT (1/pT)dN/dpT 0 0 pT pT • Rh can be less than unity. • But, insufficient to explain data TH and Y.Nara, PRC68,064902(’03)

  35. Saturation effect in d+Au? BRAHMS, PRL93,242303(’04) Cited 153 times • Forward rapidity  Small x in a nucleus • Manifestation of Color Glass Condensate?

  36. Cronin Peak  Suppression preliminary y=0,1,2,3 D.Kharzeev et al.,PRD68,094013(’03); PLB599,23(’04). H.Fujii, talk at RCNP workshop(’07) • Cronin peak disappears as moving away from • midrapidity. • Qualitatively consistent with data

  37. Di-Hadron spectra revisited STAR,PRL95,152301(’05) Cited 131 times PHENIX, PRL97,052301(’06) Cited 143 times 4.0<pT,trigger<6.0 GeV/c 0.15<pT,associated<4.0 GeV/c 2.5<pT,trigger<4.0 GeV/c 1.0<pT,associated<2.5 GeV/c • Where does the lost energy go? • Mechanism? (Mach cone? Deflected jets?)

  38. FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007) カッコ内はそのうちTOPCITE 250+

  39. No Suppression for Baryons C.Seife, Science298, 718(2002)

  40. Baryon Enhancement PHENIX, PRL91,172301(’03) Cited 126 times PHENIX, PRC69,034909(’04) Cited 268 times • Baryons are not suppressed in intermediate pT • Mechanism of enhancement?

  41. Recombination as a Third Component Soft-Soft recombination Low pT (bulk, hydro) “Third Component” Intermediate pT (~2-5 GeV/c) Recombination High pT (fragmentation) Soft-Hard Coalescence

  42. Elliptic Flow Scaling meson(n=2) q + qbar meson = baryon(n=3) q q + STAR, PRC72,014904(’05) Cited 127 times q + baryon = Voloshin(’02), Molnar, Lin(’03), Fries,Nonaka,Muller,Bass(’03),Hwa,Yang(’04),Pratt,Pal(’05)…

  43. Summary • Ｏｎｅ　ｄａｙ　ｅｘｐｅｒｉｍｅｎｔで、粒子生成メカニズムに制限をつけることができる。素朴な２成分モデルでは、ソフトな生成は９０％近い。 • 中心衝突では、エネルギー密度は十分格子ＱＣＤから予言されている臨界値を超えている。～５ＧｅＶ／ｆｍ３　＠　τ＝１ｆｍ／ｃ • 化学平衡が切れる温度は１６０ＭｅＶ程度。擬臨界温度に近い。 • 光速の５０％近い横膨張速度が得られている。大きな圧力（勾配）。 • 完全流体ＱＧＰを仮定したダイナミクスと楕円型フローの実験結果がよく合う。 • ＨＢＴ半径は流体模型では合わない。 • ミニジェットの収量は中心衝突では２０％程度まで減っており、終状態相互作用の結果である。 • 前方ラピディティでは、作られたミニジェットが減っており、ＣＧＣの発展方程式の振る舞いとコンシステント。 • 消えた後方ジェットは、マッハ錐状（？）に出ている。 • バリオンの収量は中間横運動量領域（２－６ＧｅＶ／ｃ）で減らない。楕円型フローのスケーリング的振る舞いから、クォーク再結合模型が有力。 • 個々のモデルはそれなりにうまくいっている。 • しかし、統一的な記述は未だに得られず。

  44. Talk by T.Hallman @ ICHEP04

  45. contd.

  46. Inconsistency • Some hydro model does not reproduce relative yields.  Need chemical potential for hadrons  Importance of viscosity at a hadronic level (hadronic corona) • The number of partons obtained from jet tomography is smaller than that from hydro.  Need chemical non-equilibrium process in QGP fluids. • Energy per particle from CGC is larger than data.  Need pdV work (e.g., hydrodynamic approach) • CGC gives a large eccentricity at initial state and overshoot elliptic flow data as an initial condition for ideal hydro.  Need viscosity in QGP fluids • Twice larger radial flow to understand data in intermediate pT via recombination than the one obtained from hydro simulations.  Need quantitative and dynamical anaysis of recombination mechanism • …

  47. Current Status of Dynamical Modeling Geometric Scaling CGC “DGLAP region” Before collisions Transverse momentum Shattering CGC (N)LOpQCD Parton production Pre- equilibrium fluctuation Instability? Equilibration? • Parton energy loss • Inelastic (light) • Elastic (heavy) Interaction • Hydrodynamics • viscosity • non chem. eq. “Perfect” fluid QGP or GP Recombination Coalescence Dissipative hadron gas Hadronic cascade Fragmentation Proper time Low pT Intermediate pT High pT

  48. Our studies reduce model ambiguities • TH,PRL86,2754(’01);PRC65,011901(’02).  First realistic full 3D hydro. No Bjorken boost invariant ansatz. • TH and K.Tsuda, PRC65,061902(’02).  Introduce chemical freezeout in hydro. Get correct particle ratios and spectra simultaneously for the first time. • TH and Y.Nara, PRC66,041901(’02);PRL91,082301(’03); PRC68,064902(’03);PRC69,034908(’04).  Jet quenching in QGP fluids. Realistic matter profile for jet quenching analysis. • TH and Y.Nara, NPA743,305(’04). CGC initial condition in hydro. Remove some issues for initial conditions in hydro simulations. • TH and M.Gyulassy, NPA769,71(’06); TH et al., PLB636,299(’06).  Hadronic cascade after QGP evolution. Remove issues for final decoupling.

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