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Results from RHIC Measurements of High Density Matter

Results from RHIC Measurements of High Density Matter Thomas S. Ullrich Brookhaven Nation Laboratory and Yale University January 7, 2003 Introduction Soft Physics Hard Physics (QCD) Phase Diagram of Nuclear Matter e.g. two massless flavors (Rajagopal and Wilczek, hep-ph/-0011333)

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Results from RHIC Measurements of High Density Matter

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  1. Results from RHIC Measurements of High Density Matter Thomas S. Ullrich Brookhaven Nation Laboratory and Yale University January 7, 2003 • Introduction • Soft Physics • Hard Physics

  2. (QCD) Phase Diagram of Nuclear Matter e.g. two massless flavors (Rajagopal and Wilczek, hep-ph/-0011333) • T >> LQCD: weak coupling  deconfined phase (Quark Gluon Plasma) • T << LQCD: strong coupling  confinement •  phase transition at T~ LQCD? Thomas Ullrich, BNL

  3. 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 Critical energy density: q q q q q q q q q q q q q q q q q q q q q Lattice QCD at Finite Temperature • Coincident transitions: deconfinement and chiral symmetry restoration • Recently extended to mB> 0, order still unclear (2nd, crossover ?) Ideal gas (Stefan-Boltzmann limit) F. Karsch, hep-ph/0103314 TC ~ 175 MeV  eC ~ 1 GeV/fm3 Thomas Ullrich, BNL

  4. The Phase Transition in the Laboratory soft physics regime e.m. probes (l+l-, g) hard (high-pT) probes Chemical freezeout (Tch  Tc) : inelastic scattering stops Kinetic freeze-out (Tfo Tch): elastic scattering stops Thomas Ullrich, BNL

  5. 2 concentric rings of 1740 superconducting magnets 3.8 km circumference counter-rotating beams of ions from p to Au RHIC @ Brookhaven National Laboratory BRAHMS PHOBOS Relativistic Heavy Ion Collider PHENIX STAR h Long Island • 2000 run: • Au+Au @ sNN=130 GeV • 2001 run: • Au+Au @ sNN=200 GeV (80 mb-1) • polarized p+p @ s=200 GeV (P ~15%, ~1 pb-1) Thomas Ullrich, BNL

  6. z y x Reaction plane Geometry of Heavy Ion Collisions 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 Thomas Ullrich, BNL

  7. STAR Peripheral Event From real-time Level 3 display. color code  energy loss Thomas Ullrich, BNL

  8. STAR Mid-CentralEvent From real-time Level 3 display. Thomas Ullrich, BNL

  9. STAR Central Event From real-time Level 3 display. Thomas Ullrich, BNL

  10. Charged Particle Multiplicity 19.6 GeV 130 GeV 200 GeV Central at 130 GeV: 4200 charged particles ! PHOBOS Preliminary Central dNch/dh Peripheral Total multiplicity per participant pair scales with Npart h Thomas Ullrich, BNL

  11. Energy Density at RHIC What is the energy density achieved? How does it compare to the expected phase transition value ? PHENIX EMCAL For the most central events: Bjorken formula for thermalized energy density 130 GeV time to thermalize the system (t0 ~ 1 fm/c) ~6.5 fm eBjorken~ 4.6 GeV/fm3 pR2 ~30 times normal nuclear density~1.5 to 2 times higher than at SPS (s = 17 GeV) ~ 5 times above ecritical from lattice QCD Thomas Ullrich, BNL

  12. Hydrodynamics: Modeling High-Density Scenarios • 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 • direct access to underlying physics • Works qualitatively at lower energybut always overpredicts collectiveeffects - infinite scattering limitnot valid there • RHIC is first time hydro works! lattice QCD input Thomas Ullrich, BNL

  13. purely thermal source light 1/mT dN/dmT heavy mT explosive source light T,b T 1/mT dN/dmT heavy mT RHIC Spectra - an Explosive Source • various experiments agree well • different spectral shapes for particles of differing mass strong collective radial flow • very good agreement with hydrodynamicprediction data: STAR, PHENIX, QM01 model: P. Kolb, U. Heinz Thomas Ullrich, BNL

  14. Single Particle Spectra and Radial Flow Au+Au @ 130 GeV, central and peripheral (STAR, PHENIX): Hydrodynamics even works for peripheral collisions up to b ~ 10 fm! (Heinz & Kolb hep-ph/0204061) Problem with pions at low pT  mp> 0 required p p p p p p p p K+ t = 0.6 fm/c, emax (b=0) = 24.6 GeV/fm3, <e>(t =1 fm/c) = 5.4 GeV/fm3 Tmax(b=0) = 340 MeV, Tch = 165 MeV, Tfo = 130 MeV Thomas Ullrich, BNL

  15. Tfo and <br> vs. s • <r > • increases continously • Tfo • saturates around AGS energy • Strong collective radial expansion at RHIC • high pressure • high rescattering rate • Thermalization likely Slightly model dependent here: blastwave model (Kaneta/Xu) Thomas Ullrich, BNL

  16. Azimuthal Anisotropy of Particle Emission: Elliptic Flow SPS, RHIC AGS Almond shape overlap region in coordinate space Anisotropy in momentum space Interactions v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane Thomas Ullrich, BNL

  17. Time Evolution: When Does Elliptic Flow Develop? Au+Au at b=7 fm P. Kolb, J. Sollfrank, and U. Heinz t2 t3 t1 t4 Equal energy density lines Zhang, Gyulassy, Ko, PL B455 (1999) 45 Elliptic flow observable sensitive to early evolution of system Mechanism is self-quenching Large v2 is an indication of early thermalization v2 Thomas Ullrich, BNL

  18. V2 Hydrodynamic model SPS AGS PRL 86 (2001) 402 Nch/Nmax Charged Particle v2 vs. Centrality midrapidity : |h| < 1.0 STAR PRL87 (2001)182301 Peripheral  Central Hydrodynamical models can describe data at low pT (~2 GeV/c)  compatible with early equilibration Contrast to lower collision energies where hydro overpredicts elliptical flow Thomas Ullrich, BNL

  19. Models to Evaluate Tch and B: Statistical Thermal Models • Statistical Thermal Model • F. Becattini; P. Braun-Munzinger, J. Stachel, D. Magestro • J.Rafelski PLB(1991)333; J.Sollfrank et al. PRC59(1999)1637 • Assume: • Ideal hadron resonance gas • thermally and chemically equilibrated fireball at hadro-chemical freeze-out • Recipe: • grand canonical ensemble to describe partition function  density of particles of species i • fixed by constraints: Volume V, , strangeness chemical potentialS,isospin • input: measured particle ratios • output: temperature T and baryo-chemical potential B Particle density of each particle: Qi : 1 for u and d, -1 for u and d si : 1 for s, -1 for s gi:spin-isospin freedom mi : particle mass Tch : Chemical freeze-out temperature mq : light-quark chemical potential ms : strangeness chemical potential gs : strangeness saturation factor Compare particle ratios to experimental data Thomas Ullrich, BNL

  20. Statistical Models work well at RHIC Thomas Ullrich, BNL

  21. Statistical Models: from AGS to RHIC Slight variations in the models, but roughly: Different implementation of statistical model Fact: all work well at AGS, SPS and RHIC early universe 250 RHIC quark-gluon plasma 200 Does the success of the model tell us we are dealing indeed with locally chemically equilibrated systems? this+flow  If you ask me YES! Lattice QCD Chemical Temperature Tch [MeV] SPS 150 AGS deconfinement chiral restauration 100 SIS hadron gas 50 neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Thomas Ullrich, BNL

  22. Summary on “Soft” (pT < 2 GeV/c) Physics • Particle production is large • Total Nch ~ 5000 (Au+Au s = 200 GeV)  ~ 20 in p+p • Nch/Nparticipant-pair ~ 4 (central region)  ~2.5 in p+p • Vanishing baryon/antibaryon ratio (0.7-0.8) • close to net baryon-free but not quite (net proton dN/dy~10) • Energy density is high  4-5 GeV/fm3 (model dependent) • lattice phase transition ~1 GeV/fm3, cold matter ~ 0.16 GeV/fm3 • System exhibits collective behavior (radial + elliptic flow) •  strong internal pressure that builds up very early • The system appears to freezes-out very fast • explosive expansion (HBT, correlation studies) • Particles ratios suggest chemical equilibrium • Tch170 MeV, mb<50 MeV  near lattice phase boundary • Large system at freeze-out  2  size of nuclei • Overall picture: system appears to be in equilibrium • but explodes and hadronizes rapidly Thomas Ullrich, BNL

  23. leading particle q q leading particle High-pT Particles @ RHIC – Jet Tomography Products of parton fragmentation (jet “leading particle”). Early production in parton-parton scatterings with large Q2. Direct probes of partonic phases of the reaction Sensitive to hot/dense medium: parton energy loss (“jet quenching”). Info on medium effects accessible through comparison toscaled "vacuum" (pp) yields (“binary scaling”): Production yieldscalculablevia pQCD: Thomas Ullrich, BNL

  24. 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… Thomas Ullrich, BNL

  25. Partonic Energy Loss: Theory • Elastic scattering (Bjorken 1982): • Gluon radiation is factor ~10 larger: • Thick plasma (Baier et al.): • Thin plasma (Gyulassy et al.): • Linear dependence on gluon density glue: • DE measures gluon density • DE is continuous function of energy density •  not a direct signature of deconfinement Thomas Ullrich, BNL

  26. Energy Loss in Cold Matter Wang and Wang, hep-ph/0202105 Modification of fragmentation functions in e-Nucleus scattering: dE/dx ~ 0.5 GeV/fm for 10 GeV quark Existing data is extensively studied but p+A measurements at RHIC are desperately needed  Run III (2003) d+Au Thomas Ullrich, BNL

  27. Preliminary sNN = 200 GeV High-pT Hadrons: Au+Au at RHIC Thomas Ullrich, BNL

  28. 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 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 Thomas Ullrich, BNL

  29. AA Leading Hadrons in Fixed Target Experiments Central Pb+Pb collisions at SPS p+A collisions: SPS: any parton energy loss effects buried by initial state multiple scattering, transverse radial flow,… Multiple scattering in initial state(“Cronin effect”) Thomas Ullrich, BNL

  30. 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 Thomas Ullrich, BNL

  31. 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 Thomas Ullrich, BNL

  32. Hadron Suppression: Central Au+Au (Data vs. Theory) • Parton energy loss : dE/dx ≈ 0.25 GeV/fm (expanding) dE/dx|eff ≈7 GeV/fm (static source) ~ 15 times that in cold Au nuclei • Opacities: <n> = L/≈ 3 – 4 • Gluon densities: • dNg/dy ~ 900 What does it tell us about the medium ? S.Mioduszewski PHENIX Preliminary nucl-ex/0210021 All models expect a moderate increase of RAA at higher pT Thomas Ullrich, BNL

  33. jet jet Elliptic “Flow” at High-pT: Theory Jet propagation through anisotropic matter (non-central collisions) Snellings; Gyulassy, Vitev and Wang (nucl-th/00012092) STAR @ 130 GeV • Finite v2: high pT hadron correlated with reaction plane from “soft” part of event (pT<2 GeV/c) • Finite asymmetry at high pT sensitive to energy density STAR @ 200 GeV Thomas Ullrich, BNL

  34. Dh < 0.5 Dh > 0.5 2-Particle Correlations at High-pT: Direct Evidence for Jets • Jet core: Df × Dh ~ 0.5 × 0.5  study near-side correlations (Df~0) of high pT hadronpairs • Complication: elliptic flow high pT hadrons correlated with the reaction plane (~v22) • Solution: compare azimuthal correlation functions for • Dh<0.5 (short range)  particles in jet cone + background • Dh>0.5 (long range)  background only • Azimuthal correlation function: • Trigger particle pT trig> 4 GeV/c • Associate tracks 2 < pT < pTtrig • Caveat: Away-side jet contribution • subtracted by construction, • needs different method… Near-side correlation shows jet-like signal in central Au+Au Thomas Ullrich, BNL

  35. p+p measured in RHIC detectors 0<||<1.4 unlike sign like sign p+p 2 Particle Correlations at High-pT: Back-to-Back Jets? • away-side (back-to-back) jet can be “anywhere” (Dh~2.5) • Ansatz: correlation function: high pT-triggered Au+Au event = • high pT-triggered p+p event • + • elliptic flow • + • background A: from fit to “non-jet” region Df~p/2 v2 from reaction plane analysis Thomas Ullrich, BNL

  36. Suppression of Back-to-Back Pairs Peripheral Au + Au • Near-side well-described • Away-side suppression in central • collisions STAR Preliminary STAR Preliminary near side Central Au + Au away side Away side jets are suppressed! Thomas Ullrich, BNL

  37. High pT phenomena: suppression of inclusive rates, finite elliptic flow, suppression of back-to-back pairs  compatible with extreme absorption and surface emission Thomas Ullrich, BNL

  38. ? Summary • Soft physics: • Low baryon density • System appears to be in equilibrium (hydrodynamic behaviour) • Explosive expansion, rapid hadronization • Hard physics: • Jet fragmentation observed, agreement with pQCD • Strong suppression of inclusive yields • Azimuthal anisotropy at high pT • Suppression of back-to-back hadron pairs • large parton energy loss and surface emission? • Coming Attractions: • d+Au: disentangle initial state effects in jet production • (shadowing, Cronin enhancement)  resolution of jet quenching picture • J/ and open charm: direct signature of deconfinement? • (Charm via single electrons: PHENIX, PRL 88, 192303 (2002)) • Polarized protons: DG (gluon contribution to proton spin) • Surprises … Thomas Ullrich, BNL

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