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Relativistic Heavy Ion Parallel Session Summary

This session summary discusses the bulk effects and probes observed in the QGP, including equilibration, equation of state, and hard scattered partons. The use of pQCD probes and hydrodynamics to describe the momentum distributions of bulk particles is also explored. Additionally, the connection between low-x HERA DIS physics and RHIC physics is discussed, as well as the recent theoretical efforts to extend saturation to higher Q2.

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Relativistic Heavy Ion Parallel Session Summary

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  1. 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 Relativistic Heavy IonParallel Session Summary Tim Hallman (Brookhaven National Laboratory) Jamie Nagle (University of Colorado)

  2. Bulk Effects and Probes • Bulk Effects (QGP) • 10,000 Gluons Freed • Equilibration • Equation of State • Probes of the System • Hard scattered partons • Heavy quarks Bulk system pQCD probes

  3. Hydrodynamics  Equation of State Hydrodynamics describes bulk particle momentum distributions Calculations  too long a system lifetime Enormous initial pressure, but decouples quickly (~10 fm/c)

  4. Extensive Information Almost complete reconstruction of hadronic state when system decouples. Good progress towards tracing back in time to initial conditions and Equation-of-State.

  5. Probes: QCD Factorization proton-proton Suppression Relative to Expectation in Au-Au !

  6. Gluonometer Parton traversing dense gluonic medium loses additional energy via gluon bremsstrahlung. q q

  7. Color Glass Condensate Color Quantum Liquid Parton Gas LQCD Gluon Saturation Connection of low-x HERA DIS physics and RHIC physics Distinct partons replaced by gluon wavefunction that breaks factorization Saturation in protons at x ~ 10-4 moves to x ~ 10-2 in nuclei due to additional thickness. Recent theoretical effort to extend saturation to higher Q2 (color quantum liquid)

  8. Ambiguity and a Simple Plan Au-Au Reactions deuteron-Au Reactions Factorization Expectation Last year experiments requested d-Au running to resolve this.

  9. PHENIX Preliminary 1s errors Data Rule Out Saturation Extension to x ~ 0.1 Data from PHENIX, PHOBOS and STAR show enhancement of high pT hadrons in d-A reactions (ala Cronin effect). No suppression as predicted by saturation extension. Does not rule out saturation at lower x. RdAu

  10. near side away side peripheral central Jet Correlations Back-to-back jet correlations show suppression of away side jet in Au-Au. Indicates opaque system. Deuteron-Au reactions look similar to proton-proton. Near-side jet Away-side jet

  11. A or B Many speakers stated that with extension to saturation picture ruled out, parton energy loss in dense gluonic medium is the answer. Larry McLerran said “if 10 GeV quark loses 2-3 GeV in energy in medium, it seems clear that bulk partonic matter is thermalized.” A or B (or C) HERMES electron-nucleus DIS indicate modified fragmentation which has been interpreted from fast hadronization. Modification of QCD vacuum may effect zeroth order gluon radiation. New ideas. Wealth of data needs to looked at in detail.

  12. Challenges to Picture Pions are suppressed relative to factorization, but baryons and charm mesons at intermediate pT are not.

  13. pQCD spectrum shifted by 2.2 GeV Teff = 350 MeV blue-shifted temperature Parton Recombination

  14. New Probe at RHIC: Charm and J/y PHENIX reports first J/y total cross section at collider energies! Important observable to address color singlet versus color octet production models used to address Tevatron data.

  15. pp Minimum Bias D±Kππ STAR Preliminary 0.8 pT 0.9 GeV/c |y|  0.5 |y|<0.25, 7< pT <10 GeV/c At the next CIPANP • Many more complete jet observables • Reconstruction of charm mesons • High statistics quarkonia in Au-Au • Light vector meson results • And surprises !

  16. Summary of Summary Bulk: Many indicators of fast equilibration Large initial pressure leads to fast explosion of system Probes: Medium is opaque to hard scattered light partons Moving into the realm of precision measurements. Outstanding puzzles need to be understood within simple frameworks. New data for light vector mesons and heavy flavor will add significantly. May we continue to live in exciting times!

  17. Thanks to All the Speakers • Heavy Flavor in Heavy Ions • H. Woehre • D. Silvermyr • M. Djordjevic • J. Heuser • S. Batsouli • Jet Observables • J. Jalilian Marian • I. Vitev • J. Rak • M. Miller • J. Klay • T. Chujo Extreme QCD – Probes of Gluonic Matter (Parts I and II) B. Mueller P. Jacobs L. Aphecetche G. Roland M. Gyulassy S. Bass Y. Dokshitzer L. McLerran Extreme QCD – What Equation of State? (Parts I and II) P. Steinberg Z. Xu Y. Kovchegov D. Magestro M. Lisa R. Debbe P. Kolb K. Tuchin A. Tang

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