Perspectives on RHIC-II: Heavy Ions and Hot+Dense Matter Ralf Rapp Texas A&M University 1. RHIC-II Science Workshop BNL,
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)
Thermalization at RHIC study: chiral symmetry restoration deconfinement spectral properties of matter Introduction II: Exploring the Phase Diagram 1.0 T/T c mm ‹qq› - T=1.4T c Genuine properties of QGP! Direct link to lattice QCD! [Bielefeld] LL L [Tokyo]
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
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?!
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]
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]
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]
(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 _
(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]
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
(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 !?
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 -
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 )] ----
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
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
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: ↔ 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]
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] …
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 …
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]
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]