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Exploring QCD with Heavy Ion Physics

Mark D. Baker. Exploring QCD with Heavy Ion Physics. The plan of attack - where are we?. Collide gold nuclei at high energy Is it “strongly interacting bulk matter” Collective motion Temperature, density Probe the strong interaction What we’ve learned Some puzzles

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Exploring QCD with Heavy Ion Physics

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  1. Mark D. Baker Exploring QCD with Heavy Ion Physics

  2. The plan of attack - where are we? • Collide gold nuclei at high energy • Is it “strongly interacting bulk matter” • Collective motion • Temperature, density • Probe the strong interaction • What we’ve learned • Some puzzles • Confinement, Chiral Symmetry Mark D. Baker

  3. time Kinetic freeze-out Chemical freeze-out elastic interactions inelastic interactions early universe 250 space blue beam yellow beam RHIC 200 quark-gluon plasma 150 SPS Lattice QCD AGS deconfinement chiral restauration thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Can we probe the EARLY stages? Crude estimate using t0~0.2-1 fm/c Quark Gluon Plasma? Mark D. Baker

  4. Energy Density Temperature Lattice QCD predictions e can be measured using jet dE/dx T can be measured using direct g’s Mark D. Baker

  5. leading particle q q leading particle High-pT Particles @ RHIC: “Jet Tomography” Jets are produced early in parton-parton scatterings with large Q2. Sensitive to hot/dense medium: parton energy loss(“jet quenching”). Compare leading (in pT) hadron yields to scaled pp yields (“binary scaling”): Production yieldscalculablevia pQCD + Glauber geometry Mark D. Baker

  6. Preliminary sNN = 200 GeV Preliminary sNN = 200 GeV Charged Hadron Spectra QM2002 summary talk (Peitzmann) C. Jorgensen, BRAHMS Parallel Saturday 200 GeV results from all experiments J. Klay, STAR Parallel Saturday J. Jia, PHENIX Parallel Saturday C. Roland, PHOBOS Parallel Saturday Mark D. Baker

  7. Comparing AuAu to pp A L~A1/3 # of NN collisions ~A4/3 (formally Glauber TAA(b)) # of participating nucleons: 2A Mark D. Baker

  8. N-N cross section <Nbinary>/sinelp+p Measuring Hadron Suppression 1. Compare Au+Au to nucleon-nucleon cross sections 2. Compare Au+Au central/peripheral T. Ullrich Nuclear Modification Factor: If no “effects”: R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominates Suppression: R < 1 at high-pT Mark D. Baker

  9. Leading Hadrons at CERN-SPS energies Central Pb+Pb(Au) collisions at SPS From compilation of X.N. Wang Any parton energy loss effects buried in initial state mult. scatt., transverse radial flow, etc. … Mark D. Baker

  10. p+A collisions: Caveat: The “Cronin effect” Multiple scattering in initial state: Mark D. Baker

  11. Suppression of High pT Hadrons PHENIX • AuAu data • central (0-10%) and peripheral (60-80%) • compared to N-N reference • peripheral collisions • described at high pT • central collision • suppressed at high pT Mark D. Baker

  12. Hadron Suppression: Au+Au at 130 GeV Phenix: PRL 88 022301 (2002) p0 and charged hadrons, central collisions STAR: nucl-ex/0206011 Charged hadrons, centrality dependence Clear evidence for high pT hadron suppression in central nuclear collisions Mark D. Baker

  13. yield in AuAu vs. p-p collisions D. d’Enterria Yield ratio s=200/130 GeV Consistent at at high pT with pQCD predictions (STAR) PHENIX Preliminary 70-80% Peripheral Ncoll =12.3 ±4.0 Mark D. Baker

  14. Preliminary sNN = 200 GeV Hadron Suppression: Au+Au at 200 GeV Phenix p0: peripheral and central over measured p+p STAR charged hadrons: central/peripheral PHENIX preliminary 200 GeV preliminary data: suppression of factor 4-5 persists to pT=12 GeV/c Mark D. Baker

  15. How much energy loss @ RHIC? scaled pp X.N.Wang energy loss <dE/dx> = 0.25 GeV/fm naïve 7 GeV/fm when expansion included Still under systematic study, but it’s a large effect. Mark D. Baker

  16. Another view: PHOBOS Preliminary: Au+Au 200 GeV UA1 pp (200 GeV) • Normalize by <Npart>/2 • Divide by the value at Npart=65 Mark D. Baker

  17. Hadron production ~ Npart! PHOBOS Preliminary: PHENIX nucl-ex/0207009 Au+Au 200 GeV UA1 pp (200 GeV) C. Roland, QM2002 Normalize by Npart/2. Divide by the value at Npart=65 Mark D. Baker

  18. Approximate Npart scaling is MAXIMAL jet quenching! Ncoll *S / V ~ Npart4/3 / L ~ Npart Only jets produced on the surface survive! PHENIX preliminary Ncoll Npart* Even for 8 GeV hadrons! Mark D. Baker * - not drawn by PHENIX

  19. Jets in Heavy Ion Collisions e+e- q q (OPAL@LEP) pp jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC) Hopeless task? No, but a bit tricky… Mark D. Baker

  20. Peripheral Au+Au data vs. pp+flow Hardtke, QM2002 Mark D. Baker

  21. Central Au+Au data vs. pp+flow Hardtke, QM2002 Mark D. Baker

  22. “Ratio Signal” = (AA-flow)/pp Mark D. Baker

  23. Jet suppression @ RHIC! Hardtke, QM2002 Mark D. Baker

  24. Is final state “jet quenching” the only explanation? Kharzeev, Levin, McLerran hep-ph/0210332 Particle Yield/<Npart/2> Particle Yield (spectrum) Initial state parton saturation works too ... Mark D. Baker

  25. Initial state parton saturation? See Iancu, Leonidov, McLerran hep-ph/0202270 • Gluon density cannot grow indefinitely. • Non-Abelian diagram ggg kicks in at low x or low k. Mark D. Baker

  26. “Tau scaling” in DIS 1000 stot g*p (mb) Statso et al., PRL 86 (2001) 596 100 Fit l=0.25 10 1 0.1 1 10-3 103 Mark D. Baker t Q2xl

  27. Parton Saturation “predicts” AA Kharzeev & Levin, nucl-th/0108006 • Saturated initial state gives predictions about final state. • Nh = c x Ng l~0.25 from fits to HERA data: xG(x)~x-l & t scaling Describes dN/dh shape correctly! PRL 87 (2001) Fit PHOBOS data at 130 GeV to set c, Qs Mark D. Baker

  28. Saturation Works at 200 GeV L. McLerran, DNP 2001 nucl-ex/0112001 h l~0.25 from fits to HERA data: xG(x)~x-l & t scaling Describes dN/dh energy evolution correctly! Mark D. Baker

  29. J/Y Energy/Momentum Data consistent with: Hadronic comover breakup (Ramona Vogt) w/o QGP Limiting suppression via surface emission (C.Y. Wong) Dissociation + thermal regeneration (R. Rapp) Mark D. Baker

  30. Charm Does Scale (doesn’t quench) Favors quenching interpretation for pions. Gluon radiation suppressed for heavy quarks. Dokshitzer,Kharzeev hep-ph/0106202 Mark D. Baker

  31. v2 impact parameter (fm) High pT v2 reaches geometric surface limit QM2002 (Voloshin) QM2002 (Filimonov, STAR) E. Shuryak, nucl-th/0112042 Mark D. Baker

  32. System is “black” to very high pT Adler et al., nucl-ex/0206006 Mark D. Baker

  33. Summary so far • Soft physics: • System appears to be “hydrodynamic bulk matter” • System is opaque and expanding explosively. • Naïve energy density much higher than theoretical transition • Freezeout along a universal curve near theoretical transition. • Hard physics: • Strong suppression of inclusive yields & back-to-back pairs • Azimuthal anisotropy at high pT • Open charm remains unsuppressed •  large parton energy loss and surface emission? • Caveats • d+Au needed to disentangle initial state effects in jet production • The PHENIX & PHOBOS Puzzles... Mark D. Baker

  34. p/p Tatsuya Chujo (PHENIX) p/p Central Peripheral • Proton yield is comparable with pions @ 2-4 GeV in central collisions, less in peripheral Mark D. Baker

  35. Extrapolate soft component using hydrodynamics J. Burward-Hoy • Hydrodynamic flow modifies pt threshold where hard physics starts to dominate • physics is soft (thermal) until pt 3 GeV/c Calculate spectra using hydro. parameters h+ + h - =  p, K, p Compare sum to measured Charged particle pT spectrum Mark D. Baker

  36. Important baryon and/or kaon contribution out to pT = 8 GeV/c? The PHENIX Puzzle: Mark D. Baker T. Sakaguchi, PHENIX Parallel Saturday

  37. protons p0, h Baryons at high pT Jia, Sorenson Yields scale with Ncoll near pT = 2 – 3 GeV/c Then start to fall Accident? Complex hard/soft interplay? Medium modified jet fragmentation function? Gluons and quarks “quenching” differently? Mark D. Baker

  38. The PHOBOS Puzzle nucl-ex/0211002 pQCD e+e- Calculation Mark D. Baker

  39. Different systems converge at high energy. Universality of Nch? Comparison of áNchñ vs. Energy Central Au+Au e+e- nucl-ex/0211002 pp (pp) data @ seff Central AA 1 10 102 103 s (GeV) From talk by P. Steinberg Mark D. Baker

  40. More detailed comparison of AA, ee 200 GeV e+e- measures dN/dyT(rapidity relative to“thrust” axis) Mark D. Baker

  41. early universe 250 RHIC 200 quark-gluon plasma 150 SPS Lattice QCD AGS deconfinement chiral restauration thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Universal hadronization/tranistion? LEP! Mark D. Baker

  42. Works vs. energy & centrality QM2002: nucl-ex/0212009 Need dAu data to cleanly isolate initial & final state effects! Mark D. Baker

  43. Heavy ion collisions in “target frame” UA5, Z.Phys.C33, 1 (1986) p + p inel. dNch/dh ¢/<Npart> 6% central dN/dh¢ PHOBOS Au+Au 19.6 GeV is preliminary Systematic errors not shown Mark D. Baker

  44. Summary (really!) • Very interesting state: • System appears to be “hydrodynamic bulk matter” • Initial e, T appear to be above theoretical transition. • Freezeout along a universal curve near theoretical transition. • We are beginning to probe this state: • large parton energy loss and surface emission? • Caveats and puzzles remain • Addressable with more RHIC running & detector upgrades! • Is it deconfined matter (Quark Gluon Plasma)?: • We have not achieved a clear proof yet • But Probably! Evidence is building. • Stay tuned!! Mark D. Baker

  45. Extras Mark D. Baker

  46. Interlude: Many ways to slice pz Rapidity: Generalized velocity Feynman x: scaled pz Pseudorapidity: ~y: easier to measure Mark D. Baker

  47. What is h’? Away from mid-rapidity: Mark D. Baker

  48. STAR Solenoidal field Large Solid Angle Tracking TPC’s, Si-Vertex Tracking RICH, EM Cal, TOF PHENIX Axial Field High Resolution & Rates 2 Central Arms, 2 Forward Arms TEC, RICH, EM Cal, Si, TOF, -ID Measurements of Hadronic observables using a large acceptance spectrometer Event-by-event analyses of global observables, hadronic spectra and jets Leptons, Photons, and Hadrons in selected solid angles (especially muons) Simultaneous detection of phase transition phenomena (e–m coincidences) Two “Large” Detectors at RHIC Mark D. Baker

  49. BRAHMS 2 Spectrometers - fixed target geometry Magnets, Tracking Chambers, TOF, RICH PHOBOS “Table-top” 2 Arm Spectrometer Magnet, Si -Strips, Si Multiplicity Rings, TOF Paddle Trigger Counter TOF Spectrometer Octagon+Vertex Ring Counters Inclusive particle production over a large rapidity and pT range Low pT charged hadrons Multiplicity in 4 & Particle Correlations Two “Small” Experiments at RHIC Mark D. Baker

  50. Talk by S. Manly v2 vs pseudorapidity PHOBOS: No boost invariance ! QM2002 summary slide (Voloshin) Mark D. Baker

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