1. Perspectives on RHIC-II: Heavy Ions and Hot+Dense Matter Ralf Rapp Texas A&M University 1. RHIC-II Science Workshop BNL, 19.11.04

2. Introduction I: Hot and Dense QCD + Thermal Field Theory pQCD: p>>T energy loss non-pert QCD: p~T equation of state 2GeV<p<6GeV hadronization medium probe (1) cluster (2-3) medium response (1000)  ≈20GeVfm -3 quark scaling thermal,  0 ≈0.5fm/c  D ≈0.7GeV nonabelian?! Mass/binding? phase transition? R AA (p t ) v 2 (p t /n) / n v 2 (p t,m)

3. Thermalization at RHIC  study: chiral symmetry restoration deconfinement spectral properties of matter Introduction II: Exploring the Phase Diagram 1.0 T/T c mm ‹qq› - T=1.4T c Genuine properties of QGP! Direct link to lattice QCD! [Bielefeld] LL L [Tokyo]

4. 2.) Early Phases  Matter Composition and Temperature 3.) QGP at p››T  Nonabelian Effects  Energy Deposition 4.) QGP at p~T  Degrees of Freedom and Interactions  Deconfinement 5.) Chiral Symmetry Restoration  Order Parameters and Observables  Medium Modifications of Hadrons 6.) Other Puzzles and Opportunities 7.) Concluding Remarks Outline

5. 2.) Early Matter Composition [Hirano+ Nara ‘04] Initial State: CGC!? (fwd y)  QGP (  =47cT 4 ) or GP (  =16cT 4 ) qq production (CGC, sphalerons) thermalization at  0 ≤ 0.5fm/c initial temperature Electromagnetic Diagnostics: photons and dileptons gq→  q ~ g q qq→ee ~ ( q ) 2 thermal window: q 0, M ee ≈ 1-3GeV pre-equilibrium contribution?!

6. 3.1 Energy Loss  E g /  E q =9/4 + increasing gluon content with √s 3.) Probing the QGP with high p t R AA (p t =6GeV) √s [GeV] L 2 -Dependence Already observed in DIS on nuclei [HERMES] RHIC: medium expansion + centrality dependence  L 2 Non-Abelian Charge Heavy Quarks m Q provides extra scale to disentangle, e.g., screening mass  D Energy Gauge: high-p t photon tag; R AA (p t → ∞)→1 ?! [Wang ’04] [Kharzeev+Dolshitzer, Djordjevic etal]] [Vitev ’04]

7. Cone angle of shock front cos  emis = c s /c   em =±(55º-63º)  emis [STAR] p T =(0.15-4)GeV 3.2 Energy Deposition and Correlations Track “lost” energy: thermalization? correlations as advanced tests of coalescence [Hwa etal, Fries etal] sonic shock wave in the hydrodynamic medium: [Shuryak]

8. 4.) The Thermal Nature of QGP 4.1 Light-Quark Sector Hydrodynamics requires early equilibration. How? Potential scenarios: (i) pQCD + ?! (ii) sQGP: heavy q, g + (many) boundstates (iii) q, g + (few) resonances large imaginary parts required (liquid: M~  vs. plasma:  <<T) (i) Perturbative QCD Rescattering “anomalously” large width  ~g 2 T gg↔ggg rescattering [Xu+Greiner ’04] nonabelian plasma instabilites [Moore etal ’04]

9. (ii) Heavy Partons + Multiple Bound States → based on finite-T lattice potentials approach to “zero-binding line”  ~ stable-mass  -resonance [Shuryak,Zahed, Brown, …] thermal parton scattering through bound states? composite interactions? quark scaling? Dilepton Radiation ratio to pert. qq rate M ee /m q _

10. (iii) “Hadronic” Resonances (few, colorless) “moderately” heavy q+g, rescattering above threshold; “hadron” formation above T c → generalize coalescence check with open heavy flavor dynamical origin of resonances? cc production? onset of pQCD regime: p t >5-6GeV ? open bottom? _ [Müller etal ’95, Molnar’04] [van Hees+RR ’04] Thermalization + “D”-Mesons pQCD “D” Ellitpic Flow + Coalescence jet- quench [Djordjevic etal ’04]

11. 4.2 Quarkonia: Direct vs. Regeneration QCD Lattice: J/  up to ~2T c  in QGP J/  + g c + c + X ← → -    : inelastic reaction rate (width) c-quark equilibration? Deconfinement order parameter? Width?! [Grandchamp etal] Centrality Dependence [Thews] Rapidity Spectra mc mc * y J/  Excitation Function

12. (ii) Scrutinizing Charmonium Regeneration J/  Elliptic Flow Furthermore:  Bottomonium suppression?!   ’ (sensitive to in-medium D-mesons) Suppression only Thermal Coalescence at T c [Wang+Yuan ’02] [Greco etal ’04] MB Au-Au Factor ~5 different! Transition in p t !?

13. 5.) Chiral Symmetry Restoration ~ “  - a 1 (1260)” (chiral partners) Axial-/Vector in Vacuum pQCD cont. Order parameters:, f , m q * ↔ Relation to observable? Im  em ~ [ImD  +ImD  /10+ImD  /5] Low-Mass Dilepton Rate:  -meson dominated! at T c : Chiral Restoration -

14. Hadronic Many-Body Theory 5.2 Vector Mesons at RHIC baryon effects important even at  B,net =0 : sensitive to  B,tot =   +  B, most pronounced at low M  more robust ↔ OZI - Dilepton Emission Rates Quark-Hadron Duality ?! in-med HG ≈ in-med QGP ! [qq→ee] [qq+O(  s )] ----

15. 5.3 Dileptons I: Lessons from SPS New Data (preliminary) enhancement concentrated at low (pair-) p t, theory low? signal increases with ~ (N ch ) 2 mass region between  and  8% central p t e >100MeV

16. 5.3 Dileptons II: RHIC low mass: thermal! (mostly in-medium  ) connection to Chiral Restoration: a 1 (1260)→ , 3  int. mass: QGP vs. cc → e + e - X, softening due to rescatt.? (v ┴ !) - [RR ’01] [R. Averbeck, PHENIX] QGP

17. 5.4 Resonance Spectroscopy Dilute matter, but versatile:  -meson:  m  =-50MeV and/or broad. + thermal PS + BE ?  →       : threshold strength? (   ↔  ) baryons!  ++ →   + p, N(1535)→N ,… reliable freezeout treatment (transport)  [STAR] [Florkowski etal, Brown+Shuryak] Theoretical Opportunities:  ↔ 0 ++ -glueball mixing, connects ‹qq› ↔ ‹L› interacting hadronic EoS:  (  B,T) - chem. freezeout - order parameter: D C Temperature T → Quark Mass m q → QCD m G →0 m  →0 [Fukushima]

18. 6.) (Some) Other Puzzles and Opportunities constituent quark scaling accidental? [Molnar] HBT: early QGP push + pos. x-t correlation? [Lin+Ko ‘02] exotic particles:  + [Nonaka etal ’04],  B c [Thews ‘99], glueballs ? global QGP polarization at finite b? [Wang ’04] P, CP violation (U A (1) restoration)? [Kharzeev ’04] …

19. 7.) Summary RHIC-II unique (dedicated) facility to unravel genuine (nonpert.) QCD properties of the QGP: - nonabelian energy loss (high-p t ) - bound states / resonances (IM-dileptons, open charm) - deconfinement (quarkonia; width?! J/  -regen,  -supp) - chiral symmetry restoration (LM-dileptons, resonances)  mostly rare probes (incl. excitation functions) importance of precision data + theory (redundancy) to disentangle mechanisms very exciting opportunities ahead …

20. 4.2 Direct Photons and Dileptons Sources: Initial hard scatt.: Drell-Yan / Compton (tag jets! [Gale]) Pre-equilibrium: Radiation off jets [Gale], rescatt.+fragment. of secondaries (parton cascade [Bass]) Thermal: Im Π em (M,q) Im Π em (q 0 =q) e + e - γ e.m. correlator chemical off-equilibrium: QGP: q,g ≤ 1 HG:  ,K,.. > 0 [Niemi,Moore]

21. Direct Photons at SPS and RHIC large “pre-equilibrium” yield from parton cascade (no LPM) thermal yields ~ consistent QGP undersaturation small effect pQCD Cronin ~ π 0  T 0 ≈205MeV sufficient new WA98 points:  -Bremsstr. via soft  ? [Turbide etal]