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Sampling the flavor of the Quark-Gluon Plasma.

Sampling the flavor of the Quark-Gluon Plasma. Sampling the flavour of the Quark-Gluon Plasma. QGP – Phase of matter where quark and gluons are the relevant degrees of freedom. Outline Motivation: What is the QGP? Understanding its properties The future. The bottom line.

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Sampling the flavor of the Quark-Gluon Plasma.

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  1. Sampling the flavor of the Quark-Gluon Plasma. Sampling the flavour of the Quark-Gluon Plasma. QGP – Phase of matter where quark and gluons are the relevant degrees of freedom Outline • Motivation: What is the QGP? • Understanding its properties • The future

  2. The bottom line The Relativistic Heavy Ion Collider has been operational since 2000 to study matter at extreme temperatures. Have the accelerator and experiments been successfully commissioned and operated? Yes Have we created a system that is not hadronic? Yes Have we created a weakly interacting gas of quarks and gluons (the Quark-Gluon Plasma)? No What have we created then? That’s the rest of this talk

  3. Confinement - QCD quark-antiquark pair created from vacuum Confinement: fundamental & crucial (but not understood!) feature of strong force - colored objects (quarks) have  energy in normal vacuum quark “white” 0 (confined quarks) “white” proton (confined quarks) Strong color field Force grows with separation !!! “white” proton To understand the strong force and confinement: Create and study a system of deconfined colored quarks and gluons

  4. QGP expectation came from Lattice calculations /T4 ~ # degrees of freedom deconfined: many d.o.f. confined: few d.o.f. TC ≈ 173 MeV ≈ 21012 K C  0.7 GeV/fm3 (~6x normal nuclear densities)

  5. Relativistic Heavy-Ion Collider (RHIC) PHOBOS BRAHMS RHIC PHENIX STAR AGS TANDEMS 1 km v = 0.99995c Au+Au @ sNN=200 GeV

  6. The order of the phase transition Apparently it did not ! Thus we suspect a smooth cross over or a weak first order transition “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) NASA/WMAP

  7. How we use the different quark flavors to: Outline of the rest of the talk 2. Initial State A perfect fluid? (flow) • Final State Chemical and Thermal equilibrium (Yields of particles) • Properties of the Plasma Medium’s effect on partons/hadrons

  8. Heavy-ion collision terminology z y x Reaction plane Non-central collision “peripheral” collision (b ~ bmax) “central” collision (b ~ 0) Number of participants (Npart):number of incoming nucleons (participants) in the overlap region Number of binary collisions (Nbin): number of equivalent inelastic nucleon-nucleon collisions Nbin  Npart

  9. 39.4 TeV in a central Au-Au collision Head-on Au+Au collision in STAR TPC 26 TeV is removed from the colliding beams. ~1500 charged hadrons and leptons

  10. Energy density in central Au-Au collisions Bjorken-Formula for Energy Density: Time it takes to thermalize system (t0 ~ 1 fm/c) R~6.5 fm pR2 eBJ  5.0 GeV/fm3 ~30 times normal nuclear density ~ 5 times above ecritical from lattice QCD

  11. 5 GeV/fm3. Is that a lot? Last year, the U.S. used ~100 quadrillion BTUs of energy: At 5 GeV/fm3, this would fit into a volume of: In other words, in a box of the following dimensions:

  12. Chemical equilibrium after hadronization? • Statistical Thermal Models: • Assume a system that is thermally (constant Tch) and chemically (constant ni) equilibrated • System composed of non-interacting hadrons and resonances • Obey conservation laws: Baryon Number, Strangeness, Isospin • Given Tch and  's (+ system size), ni's can be calculated in a grand canonical ensemble

  13. Chemical equilibration of hadrons Data are very well described. Tch ~ Tc Disagreement of resonances hints at significant lifetime of the hadronic phase. Au-Au √sNN = 200 GeV STAR Preliminary Strange particles also in chemical equilibrium Tch = 168 ± 6 MeV

  14. What state is the system in before hadronization? Initial state

  15. Tampa press release, April 2005 • “The truly stunning finding at RHIC that the new state of matter created in the collisions of gold ions is more like a liquid than a gas gives us a profound insight into the earliest moments of the universe. … It may well have a profound impact on the physics of the twenty-first century.” Dr. Raymond L. Orbach, Director of the DOE

  16. Applicability of hydrodynamics at RHIC • Assumes local thermal equilibrium (zero mean-free-path limit) and solves equations of motion for fluid elements (not particles) • Equations given by continuity, conservation laws, and Equation of State (EOS) • EOS relates quantities like pressure, temperature, chemical potential, volume • Most hydro calculation  no viscosity • Fluid elements  system will flow

  17. Strong collective radial expansion light 1/mT dN/dmT heavy mT Au+Au central , √s = 200 GeV T purely thermal source explosive source light T,b 1/mT dN/dmT heavy mT mT = (pT2 + m2)½ Different spectral shapes for particles of differing mass strong collective radial flow Hydro pQCD Good agreement with hydrodynamic prediction for soft EOS (QGP+HG) Tfo~ 100 MeV  bT  ~ 0.55 c

  18. Aniotropic/Elliptic flow Almond shape overlap region in coordinate space Interactions/ Rescattering Anisotropy in momentum space Elliptic flow observable sensitive to early evolution of system Mechanism is self-quenching Large v2 is an indication of early thermalization dN/df ~ 1+2 v2(pT)cos(2f) + …. f=atan(py/px) v2=cos2f v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane • M. Gehm, S. Granade, S. Hemmer, K, O’Hara, J. Thomas - Science 298 2179 (2002) Time

  19. Strong elliptic flow observed 0.2 v2(pT) 0.1 STAR preliminary 200 GeV Au+Au 0 pT (Gev/c) v2(K) > v2(L) > v2(X) Hydrodynamical models with soft Equation-of-State describe data well for pT (< 2.5 GeV/c) Compatible with early equilibration Although poor statistics even W flows - low hadronic cross-section. Evidence v2 built up in partonic phase

  20. The perfect fluid First time: hydrodynamics quantitatively describes heavy ion reactions at low pT. Prefers a QGP EOS Thermalization time t=0.6 fm/c and e=20 GeV/fm3 Hydro: small mean free path, lots of interactions NOTplasma-like Hydro without any viscosity. An ideal (perfect) fluid

  21. Microscopic picture What interactions can lead to equilibration in < 1 fm/c? Need to be REALLY strong 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 Clearly this is not the weakly coupled perturbative QGP we started looking for. s(trong)QGP 2-2 processes with pQCD s = 3 mb pT (GeV/c)

  22. Perfect fluid - caveats Hydrodynamic calculations only just gone “3D” and don’t yet fully describe the longitudinal motion. Calculations of two particle correlations are not properly described. “A theory that agrees with all available data must be wrong, since some data is always wrong.” - Sir Arthur Eddington

  23. Looking at plasma properties using “auto-generated” probes Probes of the Plasma State • Properties of the Plasma Medium’s effect on partons/hadrons

  24. pQCD calculations work in p-p Produced photons High energy probes are well described NLO perturbative QCD.

  25. Scattered partons on the “near side” lose energy, but emerge; those on the “far side” are totally absorbed Schematically partons (quarks and gluons)

  26. Scattered partons on the “near side” lose energy, but emerge; the direct photon always emerges Schematically photons

  27. pQCD in Au-Au? Compare Au+Au with p+p Collisions  RAA A+A yield Nuclear Modification Factor: p+p cross section <Nbinary>/sinelp+p R < 1 at small momenta R = 1 baseline expectation for hard processes R > 1 “Cronin” enhancements (as in pA)R < 1: Suppression

  28. RAA Au-Au central events e ~ 15 GeV/fm3 Photons p0, h from quark and gluon jets h/p0 = 0.43 (vacuum fragmentation ratio) partonic level absorption

  29. The control experiment – d-Au STAR Charge particles • d-Au - no medium - no suppression Initial state effects: - Intrinsic KT - Cronin d-Au Au-Au Suppression not caused by initial state effects

  30. Species dependence of RAA Au-Au 0-5%/40-60% Use peripheral Au-Au data since lack of available p-p All particles suppressed Baryon/meson splitting at intermediate pT

  31. Parton recombination at medium pT • Parton pT distribution is ~exponential+power-law • 7 GeV particle via : Fragmentation from high pT Meson - 2 quarks at ~4 GeV Baryon - 3 quarks at ~2.5 GeV Recombination - more baryons than mesons at medium pT

  32. Recombination and v2 The complicated observed flow pattern in v2(pT) for hadrons is predicted to be simple at the quark level pT → pT /n v2 → v2 / n , n = (2, 3) for (meson, baryon) Worksfor p, p, K0s, ,  v2s ~ v2u,d ~ 7%

  33. Suppression unique to RHIC? √sNN=62 GeV 0-5% 40-60% 0-5% 40-60% √sNN=17.3 GeV NA57, PLB in print, nucl-ex/0507012 √sNN=200 GeV See Baryon/Meson splitting even at SPS

  34. The Rcp double ratio NA57: G. Bruno, A. Dainese: nucl-ex/0511020 Baryon/meson splitting at SPS and RHIC is the same STAR Preliminary Plasma present in all systems?

  35. The heavy quark sector light ENERGY LOSS D, B c, b 1) production 2) medium energy loss 3) fragmentation M.Djordjevic PRL 94 (2004) Energy loss a) depends on properties of medium (gluon densities, size) b) depends on properties of “probe” (color charge, mass) Gluon radiation suppressed for q< m/E “Dead cone effect” • Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 Expectation: Little suppression for heavy flavor particles

  36. Detecting charm/beauty via semileptonic decays • Hadronic decay channels: Only small B.R. very hard • Non-photonic electrons: • Semileptonic channels: • c  e+ + anything (B.R.: 9.6%) • D0  e+ + anything(B.R.: 6.87%) • D e + anything(B.R.: 17.2%) • b  e+ + anything (B.R.: 10.9%) • B e + anything(B.R.: 10.2%) • Drell-Yan (small contribution for pT < 10 GeV/c) • Photonicelectron background: • g conversions (p0  gg; g  e+e- ) • p0, h, h’ Dalitz decays • r, f … decays (small) • Ke3 decays (small)

  37. Very strong suppression at high pT Non-photonic e- RAA in central Au-Au • Theory agrees only when: ignore b  e contributions very high gluon density • Is our understanding of c and b production correct? • Is our understanding of partonic energy loss correct? • How strong are the in-medium interactions? • How dense is the medium?

  38. PHENIX also measures non-photonic electron v2 Heavy quarks also flow nucl-ex/0502009 Another puzzle! Time for charm 7  larger than for light quarks (t > 10 fm/c) Greco,Ko,Rapp. PLB595, 202 (2004) Need large cross-sections - Further evidence of strong coupling

  39. Conclusions We have successfully created the Quark Gluon Plasma! - but its not what we expected when we started out Now we have many exciting properties to understand... • what causes the strong coupling? • what is the exact viscosity? • rapid equilibration? • novel hadron formation mechanisms? • what is the exact energy loss mechanism? • initial temperature determination?

  40. What about the future The Large Hadron Collider (LHC) at CERN will be commissioned in 2008 with over an order of magnitude higher energy than at RHIC. Instead of 40 TeV, 1000 TeV ! 3 experiments with dedicated heavy-ion experiments ALICE ATLAS CMS Can make more detailed measurements at the LHC

  41. Prediction from statistical model Preliminary Behavior as expected

  42. J/Y (cc) yields are suppressed Heavy quarks produced in initial violent collisions. Expect: YieldAuAu/(Nbin*Yieldpp)= 1 Suppression Factor |y|<0.35 Significant suppression of J/y in central events

  43. Quarkonia suppression  ’ ” J/Y Y’ 0.8 Tc 2 Tc 2.5 Tc Matsui & Satz (1986): Heavy quark bound states suppressed due to color screening in the QGP. Measurement of initial temperature Tdis(Y’) < Tdis(”) < Tdis(J/Y) < Tdis(’)< Tdis() T < 3 Tc or new regeneration mechanisms?

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