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What have we learned from the RHIC experiments so far ?

What have we learned from the RHIC experiments so far ?. Berndt Mueller (Duke University) KPS Meeting Seoul, 22 April 2005. Special thanks to…. The Duke QCD theory group. S.A. Bass R.J. Fries C. Nonaka T. Renk J. Ruppert M. Asakawa PRL 90, 202303 PRC 68, 044902 PLB 583, 73

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What have we learned from the RHIC experiments so far ?

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  1. What have we learned from the RHIC experiments so far ? Berndt Mueller (Duke University) KPS Meeting Seoul, 22 April 2005

  2. Special thanks to… The Duke QCD theory group • S.A. Bass • R.J. Fries • C. Nonaka • T. Renk • J. Ruppert • M. Asakawa • PRL 90, 202303 • PRC 68, 044902 • PLB 583, 73 • PRC 69, 031902 • PRL 94, 122301 … and the incredible RHIC experimental collaborations!

  3. STAR The road to the Quark-Gluon Plasma… …Is Hexagonal and 2.4 Miles Long Insights from the RHIC Experiments

  4. The quest for simplicity The equation of state of strongly interacting matter according to lattice QCD • Before the 1975, matter at high energy density was considered a mess! • QCD predicts that hot matter becomes simple – the QGP (not necessarily weakly interacting!). • Characteristic features:deconfinementandchiral symmetry restoration. Quark-gluon plasma Tc≈ 160 MeV

  5. Space-time picture of a r.h.i.c. Thermal freeze-out Hadronization Equilibration

  6. Frequently Asked Questions • How do we know that we produced equilibrated matter, not just a bunch of particles ? • What makes this matter special ? • How do we measure its properties ? • Which evidence do we have that quarks are deconfined for a brief moment (about 10-23 s) ? • Which evidence do we have for temporary chiral symmetry restoration ? • What do we still need to learn ? • Translation: When can RHIC be shut off ?

  7. FAQ #1 How do we know that we produced equilibrated matter, not just a bunch of particles ? Answer: Particles are thermally distributed and it flows !

  8. Central Au-Au √s=200 GeV STAR Preliminary Chemical equilibrium • Chemical equilibrium fits work, except where they should not (resonances with large rescattering). RHIC Au+Au @ 200 GeV • Tch = 160  10 MeV • µB = 24  5 MeV

  9. Coordinate space: initial asymmetry Momentum space: final asymmetry y Pressure gradient collective flow py px x Elliptic flow Two-particle correlations dN/d(1- 2) 1 + 2v22cos(2[1- 2])

  10. FAQ #2 What makes this matter special? Answer: It flows astonishingly smoothly ! “The least viscous non-superfluid ever seen”

  11. V2 requires ultra-low viscosity Relativistic viscous fluid dynamics: Elliptic flow from hydro with early thermalization requires h/s  0.1 D. Teaney Quantum lower bound on h/s : h/s = 1/4p (Kovtun, Son, Starinets) Realized in strongly coupled (g1)N = 4 SUSY YM theory, also in QCD ? h/s = 1/4p implies lf≈ (5 T)-1 ≈ 0.3 d QGP(T≈Tc) = sQGP

  12. FAQ #3 How do we measure its properties? Answer: With hard QCD probes, such as jets, photons, or heavy quarks

  13. High-energy parton loses energy by rescattering in dense, hot medium. q q “Jet quenching” = Parton energy loss Radiative energy loss: L Scattering centers = color charges q q Density of scattering centers g Scattering power of the QCD medium: Range of color force

  14. Phenix preliminary Peripheral collisons Central collisons Suppression of fast pions (p0)

  15. pT = 4.5 – 10 GeV/c Energy loss at RHIC • Data are described by a very large loss parameter for central collisions: (Dainese, Loizides, Paic, hep-ph/0406201) Larger than expected from perturbation theory !

  16. FAQ #4 Which evidence do we have that quarks are deconfined for a brief moment (about 10-23 s) ? Answer: Baryons and mesons are formed from independently flowing quarks

  17. Suppression Patterns: Baryons vs. Mesons • What makes baryons different from mesons ?

  18. Fragmentation Recombination Hadronization Mechanisms This is not coalescence from a dilute medium !

  19. Baryons compete with mesons Recombination “wins” … … always for a thermal source Fragmentation still wins for a power law tail

  20. R.J. Fries, BM, C. Nonaka, S.A. Bass pQCD spectrum shifted by 2.2 GeV Teff = 350 MeV blue-shifted temperature T = 180 MeV Recombination vs. Fragmentation Baryon enhancement

  21. Recombination model suggests that hadronic flow reflects partonic flow (n = number of valence quarks): Provides measurement of partonic v2 ! Hadron v2 reflects quark flow !

  22. FAQ #5 Which evidence do we have for temporary chiral symmetry restoration ?

  23. (sss) QCD mass disappears (qss) (qqs) Strangeness in Au+Au at RHIC Mass (MeV) Flavor

  24. FAQ #6: What do we still need to (or want to) learn ? • Number of degrees of freedom: • via energy density – entropy relation. • Color screening: • via dissolution of heavy quark bound states (J/Y). • Chiral symmetry restoration: • modification of hadron masses via e+e- spectroscopy. • Quantitative determination of transport properties: • viscosity, stopping power, sound velocity, etc. • What exactly is the “s”QGP ?

  25. STAR Preliminary p+p Jet-like structures (1/Ntrig) dN/d(Df) Signal Au+Au top 5% background Df Explore the interaction of an hard parton with the dense medium Associated hadrons 4 < pTtrig < 6 GeV/c , 0.15 < pTassoc < 4 GeV/c

  26. v=0.99c “Waking” the sQGP v=0.55c

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