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Quark Matter at High Density/Temperature

Quark Matter at High Density/Temperature. James C Dunlop Brookhaven National Laboratory. Defining the question. Recent Definition from STAR for the Quark Gluon Plasma.

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Quark Matter at High Density/Temperature

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  1. Quark Matter at High Density/Temperature James C Dunlop Brookhaven National Laboratory Quark Matter at High Density/Temperature James Dunlop ICHEP04

  2. Defining the question Recent Definition from STAR for the Quark Gluon Plasma QGP  a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes. Contrast with other recent definition: Approximately thermalized matter at energy densities so large that the simple degrees of freedom are quarks and gluons. This energy density is that predicted by LGT for the existence of a QGP,  2 GeV/fm3. M. Gyulassy & L. McLerran Quark Matter at High Density/Temperature James Dunlop ICHEP04

  3. RHIC Implementation PHOBOS BRAHMS &PP2PP RHIC PHENIX 1.2 km STAR • Flexibility is key to understanding complicated systems • Polarized protons, sqrt(s) = 50-500 GeV • Nuclei from d to Au, sqrt(sNN) = 20-200 GeV • Physics runs to date • Au+Au @20,62,130,200 GeV • Polarized p+p @200 GeV • d+Au @ 200 GeV Quark Matter at High Density/Temperature James Dunlop ICHEP04

  4. RHIC Experiments Four experiments, two large, two small: STAR: Large acceptance (Df = 2p, Dh = 2-6) PHENIX: Electron/muon identification, high rate trigger, limited acceptance (Df = p, Dh = 0.5 (central arm) PHOBOS: Tabletop: limited tracking acceptance, largest multiplicity acceptance of all experiments BRAHMS: Forward tracking in classical spectrometer Quark Matter at High Density/Temperature James Dunlop ICHEP04

  5. Lattice QCD Predicts a RAPID Transition in entropy density, hence pressure in heavy-quark screening mass The most realistic calcs.  no discontinuities in thermodynamic proper-ties @ RHIC conditions (i.e., no 1st- or 2nd-order phase transition), but still crossover transition with rapid evolution vs. temperature near Tc 160 – 170 MeV. in chiral condensate Quark Matter at High Density/Temperature James Dunlop ICHEP04

  6. But only smooth behavior is observed HBT parameters Charged particle pseudo-rapidity density pT-integrated elliptic flow pT-integrated elliptic flow, scaled by initial spatial eccentricity No exp’tal smoking gun!  Rely on theory-exp’t comparison Quark Matter at High Density/Temperature James Dunlop ICHEP04

  7. Chemical Equilibration? Hadron Yield Ratios STAR O PHENIX Strangeness Enhancement Resonances • pT-integrated yield ratios in central Au+Au collisions consistent with Grand Canonical stat. distribution @ Tch = (160 ± 10) MeV, B  25 MeV, across u, d and s sectors (s consistent with 1.0). • Inferred Tch consistent with Tcrit (LQCD)  T0 =~ Tcrit . • Does result point to thermodynamic and chemical equilibration, and not just phase-space dominance? Also works in e+e-, p+p Quark Matter at High Density/Temperature James Dunlop ICHEP04

  8. Collective Behavior: Azimuthal Anisotropy v2 coordinate-space-anisotropy  momentum-space-anisotropy y py px x Pressure converts initial coordinate-space Anisotropy into final momentum-space anisotropy Quark Matter at High Density/Temperature James Dunlop ICHEP04

  9. Time evolution in Ideal Hydrodynamics • Elliptic Flow reduces spatial anisotropy -> shuts itself off • Sensitive to EARLY TIMES Quark Matter at High Density/Temperature James Dunlop ICHEP04

  10. Analogy to Ultracold Atoms Extremely cold system at T=10 nK or 10^(-12) eV can produce micro-bang Elliptic flow with ultracold trapped Li6 atoms, a=> infinity regime The system is extremely dilute, but can be put into a hydro regime, with an elliptic flow, if it is specially tuned into a strong coupling regime via the so called Feshbach resonance Analogy pointed out by Shuryak Quark Matter at High Density/Temperature James Dunlop ICHEP04

  11. v2 vs. Ideal Hydrodynamics Ideal hydrodynamics reproduces v2 relatively well Below pT~2 GeV, matches v2 and spectra to ~20-30% Appealing picture: Nearly perfect fluid with local thermal equilibrium established at <~1 fm with a soft equation of state containing a QGP stage STAR Preliminary Hydro calculations: Kolb, Heinz and Huovinen Quark Matter at High Density/Temperature James Dunlop ICHEP04

  12. Score board: status of hydrodynamic models • Hadronic + QGP hydro reproduces features of v2(pT) of p, K, p • Require early thermalization (ttherm<1fm/c) + high einit > 10 GeV/fm3 • Detailed discrepancies between models and with experiment Source average Table courtesy of PHENIX Quark Matter at High Density/Temperature James Dunlop ICHEP04

  13. How unique and robust is hydro account in detail? P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev. C. C62 054909 (2000). How does sensitivity to EOS in hydro calcs. compare quantitatively to sensitiv-ity to other unknown features: e.g., freezeout treatment (compare figures at right), thermaliz’n time, longitudinal boost non-invariance, viscosity? • What has to be changed to understand HBT (below), and what effect will that change have on soft EOS conclusion? Sharp freezeout  dip Hydro+RQMD  no dip? Hydro vs. STAR HBT Rout/Rside Teaney, Lauret & Shuryak Quark Matter at High Density/Temperature James Dunlop ICHEP04

  14. Partonic energy loss in dense matter:“Jet Tomography” Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,… Multiple soft interactions: Gluon bremsstrahlung Opacity expansion: • Strong dependence of energy loss on gluon density glue: • measure DE color charge density at early hot, dense phase Quark Matter at High Density/Temperature James Dunlop ICHEP04

  15. Partonic energy loss via leading hadrons Binary collision scaling p+p reference Energy loss  softening of fragmentation  suppression of leading hadron yield Quark Matter at High Density/Temperature James Dunlop ICHEP04

  16. Control system: p+p collisions p-p PRL 91 (2003) 241803 Good agreement with NLO pQCD Parton distribution functions Fragmentation functions To generalize for nuclei: fa/N(xa,Q2,r)  fa/N(xa,Q2) . Sa/A(xa,r) . tA(r) Nuclear modification to structure function (shadowing, saturation, etc.) Nuclear thickness function p0 well described by pQCD and usual fragmentation functions p0 Quark Matter at High Density/Temperature James Dunlop ICHEP04

  17. Suppression of inclusive hadron yield RAA Au+Au relative to p+p RCP Au+Au central/peripheral PRL 91, 172302 • central Au+Au collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT Quark Matter at High Density/Temperature James Dunlop ICHEP04

  18. pQCD in Au+Au? Direct photons ( pQCD x Ncoll) / background Vogelsang/CTEQ6 ( pQCD x Ncoll) / (background x Ncoll) [w/ the real suppression] [if there were no suppression] Au+Au 200 GeV/A: 10% most central collisions Preliminary pT (GeV/c) []measured / []background = measured/background Perturbative calculation for direct photons works in central Au+Au Quark Matter at High Density/Temperature James Dunlop ICHEP04

  19. p0 RAAsSystematics Vitev, nucl-th/0404052 Cronin and parton energy loss at lower s Reasonable agreement with 62.4 GeV result. larger Cronin effect gluon dN/dy = 850 (rather than 1100) No large surprises in energy dependence PHENIX Preliminary Quark Matter at High Density/Temperature James Dunlop ICHEP04

  20. Jets at RHIC jet parton nucleon nucleon Find this……….in this p+p jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC) Quark Matter at High Density/Temperature James Dunlop ICHEP04

  21. Jets and two-particle azimuthal distributions trigger p+p  dijet • trigger: highest pT track, pT>4 GeV/c • Df distribution: 2 GeV/c<pT<pTtrigger • normalize to number of triggers Phys Rev Lett 90, 082302 Quark Matter at High Density/Temperature James Dunlop ICHEP04

  22. Azimuthal distributions in Au+Au ? Au+Au peripheral Au+Au central pedestal and flow subtracted Phys Rev Lett 90, 082302 Near-side: peripheral and central Au+Au similar to p+p Strong suppression of back-to-back correlations in central Au+Au Quark Matter at High Density/Temperature James Dunlop ICHEP04

  23. “Real” tomography: geometry of medium ? STAR Preliminary, nucl-ex/0407007 • Au+Au: Away-side suppression is larger in the out-of-plane direction compared to in-plane • Geometry of dense medium imprints itself on correlations Quark Matter at High Density/Temperature James Dunlop ICHEP04

  24. Hard Sector: Quantitative Indication of Early Gluon Density PHENIX • Inclusive hadron and away-side cor-relation suppression in central Au+Au, but not in d+Au, clearly establish jet quenching as final-state phenomenon, indicating very strong interactions of hard-scattered partons or their fragments with dense, dissipative medium produced in central Au+Au. Quark Matter at High Density/Temperature James Dunlop ICHEP04

  25. Questions for Parton Energy Loss Models • pQCD parton energy loss fits to observed central suppression  dNgluon/dy ~ 1000 at start of rapid expansion, i.e., ~30-50 times cold nuclear matter gluon density. • Large extrapolation needed to take into account time-dependent expansion • How sensitive is this result to: • assumptions of factorization in-medium and vacuum fragmentation following degradation • treatments of expansion and initial-state cold energy loss preceding hard collision? Quark Matter at High Density/Temperature James Dunlop ICHEP04

  26. Gluon Saturation: a QCD Scale for Initial Gluon Density + Early Thermaliz’n Mechanism? PHOBOS, PRC 65, 061901R BRAHMS, nucl-ex/0403005 sNN = 130 GeV Au+Au • Does the high initial gluon density inferred from parton E loss fits demand a deconfined initial state? Can QCD illuminate the initial conditions? • Assuming initial state dominated by g+g below the saturation scale (con-strained by HERA e-p), Color Glass Condensate approaches ~account for RHIC bulk rapidity densities  dNg/dy ~ consistent with parton E loss. • Rapidity dependence of RdA consistent, though questions about uniqueness • Remaining questions about robustness and uniqueness of approach Quark Matter at High Density/Temperature James Dunlop ICHEP04

  27. Unusual behavior in baryons Large enhancement in baryons at intermediate pT Not explainable in vacuum fragmentation framework Quark Matter at High Density/Temperature James Dunlop ICHEP04

  28. Intermediate pT: hints of relevant degrees of freedom Clear separation into two classes: baryons and mesons Apparent scaling with number of constituent quarks in final-state hadron Explained currently by recombination/coalescence of constituent quarks at hadronization If better established, direct evidence of the degrees of freedom relevant at hadronization, and the existence of collective flow at the constituent quark level STAR Preliminary, nucl-ex/0403032 v2/nq Quark Matter at High Density/Temperature James Dunlop ICHEP04

  29. Jet-like correlations at intermediate pT PHENIX Preliminary, nucl-ex/0408007 • jet partner equally likely for trigger baryons & mesons • Same side: slight decrease with centrality for baryons • Larger partner probability than pp, dAu • Away side: partner rate as in p+p confirms jet source of baryons! • “disappearance” of away-side jet for both baryons and mesons Quark Matter at High Density/Temperature James Dunlop ICHEP04

  30. Questions for Coalescence Models Duke-model recomb. calcs. Duke-model recomb. calcs. • Can one account simultaneously for spectra, v2 and di-hadron  correlations at intermediate pT with mixture of quark recombination and fragmentation contributions? Do observed jet-like near-side correlations arise from small vacuum fragmentation component, or from “fast-slow” recombination? • Are thermal recomb., “fast-slow” recomb. and vacuum fragment-ation treatments compatible? Double-counting, mixing d.o.f., etc.? Quark Matter at High Density/Temperature James Dunlop ICHEP04

  31. Five Observations Ideal hydro Early thermalization + soft EOS Statistical model Quark recombination constituent q d.o.f. …suggest appealing QGP-based picture of RHIC collision evolution, BUT invoke 5 distinct models, each with own ambiguities, to get there. u, d, s equil-ibration near Tcrit pQCD parton E loss CGC Very high inferred initial gluon density Very high anticipated initial gluon density Quark Matter at High Density/Temperature James Dunlop ICHEP04

  32. Summary • RHIC has made major advances in runs 1-3, leading to an appealing picture of bulk, dense, highly interacting matter. • Extended reach in energy density appears to reach simplifying conditions in central collisions -- ~ideal fluid expansion; approx. local thermal equilibrium. • Extended reach in pT gives probes for behavior difficult to access at lower energies – jet quenching; ~constituent quark scaling. • However: In the absence of a direct “smoking gun” signal of deconfinement revealed by experiment alone, a QGP discovery claim must rest on the comparison with a promising, but still not yet mature, theoretical framework. In this circumstance, clear predictive power with quantitative assessments of theoretical uncertainties are necessary for the present appealing picture to survive as a lasting one. Quark Matter at High Density/Temperature James Dunlop ICHEP04

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