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PHENIX Overview: Status of QGP

PHENIX Overview: Status of QGP. Terry C. Awes Oak Ridge National Laboratory IX Workshop on High Energy Physics Phenomenology Jan. 3-14, 2006 Bhubaneswar, India. Quark Gluon Plasma. F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004).

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PHENIX Overview: Status of QGP

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  1. PHENIX Overview: Status of QGP Terry C. Awes Oak Ridge National Laboratory IX Workshop on High Energy Physics Phenomenology Jan. 3-14, 2006 Bhubaneswar, India

  2. Quark Gluon Plasma F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004) • Lattice QCD predicts transition to deconfined Quark Gluon Plasma phase at ~175MeV • Goal of Relativistic Heavy Ion collisions - to produce and characterize QGP state.

  3. Hadronization (Freeze-out) + Expansion Pre-equilibrium Thermalization QGP phase? Mixed phase g, g* e+e-, m+m- p, K, p, n, f, L, D, X, W, d,… Soft hadrons reflect medium properties when interactions stop (chemical and thermal freeze-out). Hard processes (early stages): Real and virtual photons, high pT partons. PHENIX emphasis Central Relativistic Heavy Ion Collision

  4. Studying high density matter with Relativistic Heavy Ion Collisions • Does the produced matter in RHI reach local equilibrium - allowing a discussion of “matter properties” ? • Is deconfined “quark matter” produced? • What is the transition temperature? • What are the characteristics of the quark matter? • Opacity • Viscosity • Heat capacity - Degrees of freedom - quarks and gluons or more complicated colored objects? • etc What have we learned so far?

  5. Hadron measurement |h|<0.35 PID using TOF p/K/p separation up to 2 GeV/c (EMCAL) and 4 GeV/c (TOF) Electron measurement |h|<0.35 PID using RICH e/p separation up to pT ~ 4.8 GeV/c Photon measurement |h|<0.35 Two different calorimeters PbSc and PbGl PID using TOF, shower shape, charged veto Muon measurements 1.2 < |h| < 2.4 Two separate arms at forward and backward rapidity PHENIX detector at RHIC

  6. Spectator nucleons Participant nucleons Centrality: Nucleon Collisions & Nucleon Participants Spectator neutrons 10-15% 5-10% 0-5% Peripheral Central Forward Mult. • Centrality selection : Sum of Beam-Beam Counter • (BBC, |h|=3~4) and energy of Zero-degree calorimeter (ZDC) • ExtractedNcollandNpart based on Glauber model.

  7. The Final State: Particle Yields Assuming Chemical Equillibrium: (Chemical Freeze-Out) Braun-Munzinger, Maegestro, and Stachel • Excellent description of relative yields of particles with only 2 parameters.

  8. QGP to Hadron Phase transition? • Chemical Freeze-Out Temperature (at mB) is remarkably close to the Hadron to QGP phase boundary predicted by Lattice QCD. • How can chemical equillibrium be attained so rapidly? (Hadronic rates/cross sections too small -- equilibrated in partonic phase?). Why is TChem so high?

  9. PHENIX (PRC72 2005 014903) The Final State: Thermal Freeze-Out Particle Spectra Central Au+Au T=109MeV bT(Max)=0.77 • Particle Spectra p,K,p,f (“low” pT) can be described consistently with common Temperature and radial flow velocity profile (max. bT )

  10. PHENIX Preliminary Peripheral Central The Final State: Thermal Freeze-Out • Particle Spectra (p,K,p,f) can be described consistently with common T and radial flow bT that depends on overlap volume. • Increase in centrality (volume) gives longer lifetime - more rescattering allows transfer from thermal to collective motion, thus larger bT and lower T. • Results suggest significant rescattering. Pressure? Thermalization? Temperature <bT>

  11. Study via angular (f) correlations between particle and event plane (average F), or between particle pairs. z y x   Anisotropic Flow: aka Elliptic Flow • For non-zero impact parameter, the nuclear overlap volume is f-asymmetric. • If the matter interacts strongly, pressure gradients will result and the initial spatial asymmetry will be converted to a momentum asymmetry. Elliptic flow = v2 = 2nd Fourier coefficient of azimuthal anisotropy

  12. Jet Function Correlation Function In-plane Out-of-plane V2 Harmonic Elliptic Flow via 2-particle correlation 2-particle correlation with trigger particle selected according to event plane measured in forward rapidity region (BBC). R(f) Azimuthal Correlations include elliptic flow and di-jet contributions f More about jet component later …

  13. Final State: Elliptic Flow PHENIX Preliminary Observed large v2 implies strong interactions in the produced matter. From Hydro: • Observe v2 dependent on pT and particle mass • Such dependences expected from hydro (flow)

  14. Final State: Putting it together One can obtain a consistent description of the final state -- particle spectra, yields, azimuthal asymmetries, and radii (from p-p HBT analyses) using a hydro inspired “Blastwave” model (F. Retiere, nucl-ex/0404024). Au+Au 200 GeV T=106 ± 1 MeV <bInPlane> = 0.571 ± 0.004 c <bOutOfPlane> = 0.540 ± 0.004 c RInPlane = 11.1 ± 0.2 fm ROutOfPlane = 12.1 ± 0.2 fm Life time (t) = 8.4 ± 0.2 fm/c Emission duration = 1.9 ± 0.2 fm/c c2/dof = 120 / 86

  15. QGP to Hadron Phase transition? • Particle Yields: Chemical Freeze-Out at T~175MeV and mB ~ 30 MeV. ??? • Consistent description of final state indicates that system lives ~10fm/c, with pion emission occurring in a final burst of ~2fm/c duration at T~100MeV • Did system initially enter QGP phase? How far -what T?

  16. PHENIX Huovinen et al Probing the Early Phase: Theory • Ideal Hydrodynamics (1+1Dim) can describe the particle spectra and v2 if Equation of State includes QGP phase. EOS without QGP too hard. • Parton Cascade (Boltz.Eq.) requires unphysically large cross sections (~45mb). Why? • Suggests initial matter of Quarks and Gluons is strongly interacting (sQGP) and non-viscous (Ideal Hydro). “Perfect Liquid” • Large initial energy density: ~15-25 GeV/fm3 (çrit~1GeV/ fm3)

  17. Perfect Liquid: h/s=1/4p h/s=1/4p

  18. Press release based on RHIC “White Papers” PHENIX (Nucl. Phys. A757, 2005 I&II): Model comparisons show Hydro+ChemEq doesn’t work, Hydro+HadronCascade is better. p p elliptic flow PHENIX white paper, NPA757,184(2005) pT spectra

  19. h/s=1/4p State of the Art: CGC+3D hydro+hadron cascade (Hirano et al) Reproduces all quite well including rapidity dependence of v2 for non-peripheral collisions. h : shear viscosity, s : entropy density Its ratio to entropy density Absolute value of viscosity It’s because h/s is small that Ideal Hydro works so well. Hirano & Gyulassy, nucl-th/0506049

  20. Probing the Early Phase: Back to experiment… • If initial phase is thermalized it should radiate photons. Measure the initial temperature via the spectrum of thermal photon radiation. If you measure T0 much greater than TC one can be sure to have started in QG phase. • Study production of hard probes produced early in the collision to deduce properties of the produced medium that they must traverse • Jets, i.e. hard scattered partons. More particularly high pT particles from jet fragmentation. • Charm production • J/y production

  21. Photons: Continum Spectrum with Many Sources Rate +Weak+EM decay g’s (p0,h) = Bkgd Hadron Gas Thermal Tf QGP Thermal Ti Pre-Equilibrium Jet Re-interaction Turbide, Rapp, Gale Final-state photons are the sum of emissions from the entire history of a nuclear collision. pQCD Prompt Eg

  22. p0 and h - On the way to Measuring Direct g in s=200 GeV/c Au+Au collisions • Measure p0 and h distributions- • Input to MC to calculate decay g • Compare measured g to decay g to extract direct g yield Au-Au PRL 91 072301 h Spectra Centrality PHENIX Preliminary

  23. Large contribution from gluon fragmentation. Calculations with different (gluon) FF’s (Regions indicate scale uncertainty) High-PTp0 spectra in p+p collisions at 200 GeV/c Spectra forp0 out to 12 GeV/c compared to NLO pQCD predictions (by W.Vogelsang) pQCD works very well! p-pPRL 91(2003) 241803

  24. High-pTg in p+p (d+Au) Collisions at 200 GeV/c As observed for p0 production, the direct photon measurement in p+p agrees with NLO pQCD calculations. The preliminary d+Au g yield also agrees with <Ncoll> -scaled NLO pQCD calculation. Baseline for comparison with Au+Au g results.

  25. First RHIC Au+Au Direct Photon Results • Direct g excess consistent with NLO pQCD p+p predictions, scaled by the number of binary collisions. • Fragmentation?, Bremsstrahlung?, Thermal? PHENIX PRL 94, 232301 (2005)

  26. Centrality Dependence of Direct Photons • Within errors <Ncoll> scaled NLO pQCD describes g yield even to low pT ! • Need to improve errors on p+p and Au+Au measurements to search for deviations from pQCD as evidence for other contributions, e.g. thermal g PHENIX PRL 94, 232301 (2005)

  27. Thermal Photon Expectations? • Hydrodynamical predictions for thermal g (HRG + QGP) plus prompt NLO pQCD prediction yields. • Consistent with thermal with QGP with T0 of 590MeV. • Measured g yield is consistent with NLO pQCD prediction with or without thermal contribution. • NLO pQCD works too well!? Fragmentation g contributions are large (~50% at 3 GeV/c, 35% at 10 GeV/c). Why not modified? Central Au+Au d’Enterria and Peressounko nucl-th/0503054

  28. PHENIX preliminary Thermal Photons: Initial Temperature • Preliminary result from higher statistics Run4 data set. Different method. • Can the errors on the data, pQCD and thermal model calculations be reduced sufficiently to deduce initial temperature? Probably not... • Can deduce that the photon yield is consistent with various predictions with T0max ~ 500-600 MeV T0ave ~ 300-400 MeV

  29. Spectators Participants AA AA “Nominal effects”: R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominates AA AA AA Suppression: R < 1 at high-pT kT broadening (Cronin): R > 1 AA AA Hard Probes: Nuclear Effects? Nuclear Modification Factor: Compare A+A to p+p cross section

  30. Large suppression (factor of 5 - huge “nuclear effect”!) implies large energy loss, implies high initial densities… Strong Suppression! Centrality Dependence RAA for p0 and charged hadrons Suppression increases with increasing nuclear overlap volume. Increasing density and pathlength. (Difference between p0 and charged hadrons due to contributions from protons - more later) PHENIX AuAu 200 GeV p0 data: PRL 91 (2003) 072301. charged hadron: PRC 69 (2004) 034909.

  31. schematic view of jet production leading particle hadrons q q hadrons leading particle Quenching of Hard Scattered Partons • Hard parton scatterings in nucleon collisions produce jets of particles. • In the presence of a dense strongly interacting medium, the scattered partons will suffer soft interactions losing energy (dE/dx~GeV/fm). • Softer fragmentation spectrum: “Jet Quenching” Alternatively, reduced hard scattering rate due to initial state PDF modification? “Gluon Saturation”

  32. Large suppression implies large energy loss. Model calculations indicate high gluon densities dNg/dy ~ 1100 • Implieslarge energy density(as do also ET measurements) e > 10 GeV/fm3 wellabove critical energy densityecrit ~ 1 GeV/fm3 Strong Suppression! Theoretical Interpretation of High-pTπ0 Suppression

  33. A Closer Look at pT Dependence of Direct Photons and p0 Production for Central Au+Au • High pTg yield consistent with binary scaled pQCD in contrast to factor of 5 suppression of p0 & h yields. PHENIX PRL 94, 232301 (2005) • Direct g are not suppressed - strong evidence that hadron suppression is due to final state, i.e. parton energy loss.

  34. Baryon “Anomaly” • While p0 show strong high pT suppression, high pT protons seem not to be suppressed. • Surprising result if p and pbar produced from fragmentation. • f shows suppression similar to pions. Not a “mass effect”. Can be explained as a quark recombination effect (thermal+fragmentation quarks) - strong evidence that quark matter has been formed.

  35. Quark Scaling of Elliptic Flow (v2) • Scale baryon/meson v2 and pT by number of quarks (nq = 3, 2). • Observe near universal scaling (better if account for decay contribution to pions). • Strongly suggests that collective flow develops during the quark phase.

  36. Greco,Ko,Rapp: PLB595(2004)202 Even heavy quarks flow… • “Measure” Charm via single electrons after subtracting photon conversion contribution. • Recombination model indicates that the charm quark itself flows at low pT. • Charm flow supports high parton density and strong coupling in the matter. It is not a weakly coupled gas. • Drop of v2 at high pT perhaps due loss of collectivity or to b-quark contribution.

  37. (1) q_hat = 0 GeV2/fm (4) dNg / dy = 1000 (2) q_hat = 4 GeV2/fm (3) q_hat = 14 GeV2/fm Heavy Quarks also lose energy • “Measure” Charm via single electrons after subtracting photon conversion contribution. • Even heavy quark (charm) suffers substantial energy loss in the matter. • The data suggest large c-quark-medium cross section; evidence for strongly coupled QGP? • The data provide a strong constraint on energy loss models. Theory curves: (1-3) from N. Armesto, et al., hep-ph/0501225 (4) from M. Djordjevic, M. Gyulassy, S.Wicks, PRL. 94, 112301

  38. J/y Suppression: System Size Dependence • Models that were successful to describe SPS data assuming disociation in QGP or by comovers fail to describe data at RHIC. • Predict too much suppression!

  39. J/y Suppression: System Size Dependence • The preliminary data are in better agreement with models with the predicted suppression + re-generation (quark recombination) at the energy density of RHIC collisions. • Can be tested by measurement of v2(J/y)?

  40. Di-jet analyses: just a taste… • Di-jet tomography is a powerful tool to probe the matter - study yields, widths, pT , and centrality dependence. • The shapes of jets are modified by the matter. • Mach cone? • Cerenkov? • Flow? • Can the properties of the matter be measured from the shape? • Sound velocity • Dielectric constant PHENIX preliminary

  41. Summary and Conclusions • Although there is no “smoking gun” signature for deconfined (QGP) matter, there is now a large body of data that provides many model constraints. We’re on the way towards development of a “Standard Model” of RHI collisions (eg. CGC+3D Hydro + Hadron Cascade). • Some experimental observations and inferences at RHIC: • Produced matter is strongly interacting: large collective flow and parton energy loss, including charm. • Locally thermalized: very likely because of above and success of Hydro interpretation. • Quark Gluon phase: very likely per success of quark recombination interpretation of baryon anomaly, flow. • Much more to come…

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