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Search for the Quark Gluon Plasma: A Status Report

Search for the Quark Gluon Plasma: A Status Report. J. Nagle University of Colorado. Phase Diagram of Nuclear Matter. What is the Quark Gluon Plasma?. F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004).

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Search for the Quark Gluon Plasma: A Status Report

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  1. Search for the Quark Gluon Plasma:A Status Report J. Nagle University of Colorado

  2. Phase Diagram of Nuclear Matter

  3. What is the Quark Gluon Plasma? F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004) Lattice QCD reveals a rapid increase in the degrees of freedom associated with the deconfinement of quarks and gluons. Transition point: T ~ 170 MeV e ~ 1.0 GeV/fm3 Screening of long-range confining potential

  4. No. Strong Coupling as ~ 0.5 for T~ 1.5 Tc Quasiparticles may be dressed partons or plasmons or none. q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q Coupling Strength Is the Quark Gluon Plasma a free gas of nearly massless quarks and gluons?

  5. Phase Transition Order? ? Physical Point Strange Quark Mass Light Quark Mass

  6. Apparently it did not ! This supports a smooth cross over or a weak first order transition Early Universe “A first-order QCD phase transition that occurred in the early universe would lead to a surprisingly rich cosmological scenario.” Ed Witten, Phys. Rev. D (1984)

  7. RHIC is doing great ! STAR The Experiment • Relativistic Heavy Ion Collider online since 2000. • Design Gold Gold energy and luminosity achieved. • All experiments successfully taking data • Polarized proton proton (spin) program also underway

  8. In the Laboratory 10,000 gluons, quarks, and antiquarks from the nuclear wavefunctions are made physical in the laboratory !

  9. BRAHMS Energy Energy deposition determined by measuring spectator nucleons. Out of 39.4 TeV maximum energy, at least 26 TeV is made available for heating the fireball. Transverse energy indicates initial energy density well above the transition value.

  10. PHOBOS Collective Motion • In non central collisions, large initial spatial anisotropy • The degree to which this translated into momentum space is an excellent measure of the pressure

  11. Hydrodynamic Behavior Starting with initial conditions, hydrodynamic calculations with zero viscosity reasonably describe the data. v2 pT (GeV) Equilibration time t=0.6 fm/c and e=20 GeV/fm3

  12. Near-Perfect Fluid Motivated by AdS/CFT calculated lower viscosity bound ? Critical goal to put the QGP data point on this plot

  13. Microscopic Picture to Hydrodynamics Hadronic transport models (e.g. RQMD, HSD, ...) with hadron formation times ~1 fm/c, fail to describe data. Hydrodynamic STAR PHOBOS HSD Calculation pT>2 GeV/c RQMD What interactions can lead to equilibration in < 1 fm/c? Clearly the system is not a hadron gas. Not surprising.

  14. Perturbative calculations of gluon scattering lead to long equilibration times (> 2.6 fm/c) and small v2. R. Baier, A.H. Mueller, D. Schiff, D. Son, Phys. Lett. B539, 46 (2002). MPC 1.6.0, D. Molnar, M. Gyulassy, Nucl. Phys. A 697 (2002). v2 2-2 processes with pQCD s = 3 mb pT (GeV/c) Microscopic Picture to Hydrodynamics What interactions can lead to equilibration in < 1 fm/c? Clearly this is not a perturbative QGP. Not surprising.

  15. Plasma Instabilities Exponential growth of color fields due to instabilities. Very rapid isotropization. Rapid thermalization is still a mystery, but with exciting possible explanations. Scaled Field Energy Density

  16. solid: STAR open: PHENIX PRL91(03) We find an interesting scaling with the constituent quark number. Perhaps an indication of "dressed" quarks coalescing to form hadrons. Hadronization Even the heavy f, X, W show large flow. At high pT, they deviate from hydrodynamics.

  17. Probing the Medium Sometimes a high energy photon is created in the collision. We expect it to pass through the plasma without pause.

  18. Color Probes of the Medium Sometimes we produce a high energy quark or gluon. If the plasma is dense enough we expect the quark or gluon to be swallowed up.

  19. Very Opaque Medium Scaling of photons shows excellent calibrated probe. Quarks and gluons disappear into medium, except consistent with surface emission. Photons Survival Probability p0, h from quark and gluon jets

  20. Jet correlations in proton-proton reactions. Strong back-to-back peaks. Jet correlations in central Gold-Gold. Away side jet disappears for particles pT > 2 GeV Jet correlations in central Gold-Gold. Away side jet reappears for particles pT>200 MeV Jet Quenching! Azimuthal Angular Correlations

  21. 3 Particle Correlation measure may hint at different underlying physics. Au+Au 10% Dφ2=φ2-φtrig dN2/dΔφ1dΔφ2/Ntrig Dφ1=φ1-φtrig Reaction of the Medium Extreme distortion of jets. Is this a shock wave propagating through the medium? Reflected Distribution

  22. Heavy Quarks Naive assumption is that heavy quarks are too massive to quickly thermalize in medium. Suppression Factor If interactions are strong enough, prediction is for large push of charm to low pT and large v2 anisotropy.

  23. Full D Reconstruction in Heavy Ions Reactions! PHENIX Preliminary Charm Results Single non-photonic electrons tell us about D and B mesons. Thus, even heavy quarks are pushed along with the medium. Key measure to help pin down viscosity.

  24. Suppression Factor Heavy Quarkonia We expect a suppression of bound states due to color screening in the Quark Gluon Plasma. J/y are suppressed. But not as much as expected if we have complete color screening.

  25. Perhaps charm recombination creates new J/y later. Data to prove or disprove this explanation is on tape. Resolving the Puzzle Recent Lattice QCD results indicate J/y spectral function may persist up to 3 Tc. Temperature Bound < 3 Tc (?) J/y

  26. Thermal Radiation? New method for heavy ion reactions of measuring virtual photons allows one to subtract away p0 and h decay contributions. First results show indication of photon radiation above NLO pQCD initial scattering contribution. Working towards a temperature determination.

  27. NA60 and Low Mass Pairs Low mass dileptons give us a probe of the interactions in the hot dense early phase. e- e+ Key next measurement at RHIC

  28. Conclusions • We have successfully created • the Quark Gluon Plasma! • Now we have many exciting • properties to understand... • low viscosity • rapid equilibration • novel hadron formation mechanisms • jet quenching and medium reaction • temperature determination • degrees of freedom

  29. Very significant cuts in basic research in the Department of Energy Office of Science are being proposed. It is hard for me to imagine a world where we stop asking the big questions or stop trying to answer them. Fight the Future

  30. Extra Slides

  31. Signatures of the QGP

  32. <pt> Fluctuations ? Physical Point We must study properties of the medium in detail without a smoking gun phase transition signature. Smooth Cross Over? Observables show a smooth energy dependence. Source Emission Size

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