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Hard probes of hot, dense matter at RHIC

Hard probes of hot, dense matter at RHIC. Report from PHENIX. Barbara V. Jacak Stony Brook Feb. 19, 2004. outline. Introduction to PHENIX & our physics approach Talk covers only a subset of PHENIX results! Elliptic flow: magnitude and flavor dependence of v 2 Jets in pp, dAu and AuAu

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Hard probes of hot, dense matter at RHIC

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  1. Hard probes of hot, dense matter at RHIC Report from PHENIX Barbara V. Jacak Stony Brook Feb. 19, 2004

  2. outline • Introduction to PHENIX & our physics approach • Talk covers only a subset of PHENIX results! • Elliptic flow: magnitude and flavor dependence of v2 • Jets in pp, dAu and AuAu • Suppression and non-suppression • pT distribution of partons • a closer look at Au+Au • Baryons and jet fragmentation • Heavy quark production

  3. vacuum QGP did something new happen at RHIC? • Study collision dynamics (via final state) • Probe the early (hot) phase Equilibrium? hadron spectra, yields Collective behavior i.e. pressure and expansion? elliptic, radial flow Particles created early, predictable quantity, interact differently in QGP vs. hadron matter fast quarks/gluons, J/Y, D mesons thermal radiation

  4. p-p hep-ex/0304038 Good agreement with NLO pQCD Parton distribution functions Fragmentation functions s = 200 GeV, hard probesstart with pQCD & pp collisions Works! A handle on initial NN interactions by scattering of q, g inside N We also need: p0

  5. EOS Tc ~ 170 ± 10 MeV (1012 °K) e ~ 3 GeV/fm3 Lattice QCD says: Create these conditions to look for new physics In A+A: QCD in non-perturbative regime Lattice… we look for physics beyond simple superposition of NN: Equilibration Collective effects Energy, color transport in dense medium Deconfinement? Physics is soft! Karsch, Laermann, Peikert ‘99 e/T4 T/Tc

  6. PHENIX at RHIC 2 Central spectrometers 2 Forward spectrometers 3 Global detectors

  7. Brazil University of São Paulo, São Paulo China Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, Beijing France LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecòle des Mines at Nantes, Nantes Germany University of Münster, Münster Hungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, Bombay Israel Weizmann Institute, Rehovot Japan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY University of Tokyo, Bunkyo-ku, Tokyo Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, Seoul Russia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg St. Petersburg State Technical University, St. Petersburg Sweden Lund University, Lund 12 Countries; 57 Institutions; 460 Participants USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida State University, Tallahassee, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

  8. Colliding system expands: Energy  to beam direction per unit velocity || to beam pR2 • e 5.5 GeV/fm3 (200 GeV Au+Au) 2ct0 well above predicted transition! Is the energy density high enough? PRL87, 052301 (2001)

  9. ( pQCD x Ncoll) / background Vogelsang/CTEQ6 ( pQCD x Ncoll) / (background x Ncoll) [w/ the real suppression] [if there were no suppression] pQCD in Au+Au? direct photons At high pT, it also works! gTOT/gp0 Au+Au 200 GeV/A: 10% most central collisions Preliminary pT (GeV/c) []measured / []background = measured/background

  10. Almond shape overlap region in coordinate space Pressure? “elliptic flow” barometer Origin: spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system spatial anisotropy  momentum anisotropy v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane

  11. min bias 200 GeV Au+ Au PHENIX measures v2 two ways: • 2 particle correlations • Gets tricky at high pT, jets can contribute • Determine reaction plane at y = 3-4 • From BBC, with full azimuthal symmetry • Measure hadrons in central arms, sort vs. reaction plane • No jet effects upon found reaction plane

  12. Implication #1 of fast equilibration & large v2 Huge cross sections!!

  13. p above p for • pT < 2 GeV/c. • Then crosses over • Values ~ saturate • at high pT • geometry? • v2/quark seems • almost constant •  create hadrons • by coalescence of • quarks from • boosted distribution? Implication #2 (from flavor dependence) nucl-ex/0305013

  14. schematic view of jet production hadrons leading particle q q hadrons leading particle a unique probe for physics of hot medium Probe: Jets from hard scattered quarks Observed via fast leading particles or azimuthal correlations between the leading particles • But, before they create jets, the scattered quarks radiate energy (~ GeV/fm) in the colored medium • decreases their momentum (fewer high pT particles) • “kills” jet partner on other side • “jet quenching”

  15. AA AA If no “effects”: RAA < 1 in regime of soft physics RAA = 1 at high-pT where hard scattering dominates Suppression: RAA < 1 at high-pT AA Nuclear Modification of Leading Part. Spectra? 1. Compare Au+Au to nucleon-nucleon cross sections 2. Compare Au+Au central/peripheral Nuclear Modification Factor: nucleon-nucleon cross section <Nbinary>/sinelp+p

  16. Au-Au s = 200 GeV: high pT suppression! PRL91, 072301(2003)

  17. Suppression: a final state effect? Hadron gas • Hadronic absorption of fragments: • Gallmeister, et al. PRC67,044905(2003) • Fragments formed inside hadronic medium • Energy loss of partons in dense matter • Gyulassy, Wang, Vitev, Baier, Wiedemann… Absent in d+Au collisions! d+Au is the “control” experiment

  18. probe rest frame r/ ggg Suppression: an initial state effect? • Gluon Saturation • (color glass condensate) Wavefunction of low x gluons overlap; the self-coupling gluons fuse, saturating the density of gluons in the initial state.(gets Nch right!) • Initial state elastic scattering (Cronin effect) Wang, Kopeliovich, Levai, Accardi • Nuclear shadowing Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan, Balitsky, Kovchegov, Kovner, Iancu … RdAu~ 0.5 D.Kharzeev et al., hep-ph/0210033 Broaden pT :

  19. Compare centrality dependence to control Au + Au Experiment d + Au Control • Dramatically different and opposite centrality evolution of AuAu experiment from dAu control. • Jet suppression is clearly a final state effect.

  20. Centrality dependence of Cronin effect • Probe response of coldnuclear matter with increased number of collisions. • See larger Cronin effect for baryons than for mesons (as at Fermilab) Qualitative agreement with model by Accardi and Gyulassy. Partonic Glauber-Eikonal approach: sequential multiple partonic collisions. nucl-th/0308029

  21. Pions in 3 detectors. • Charged pions from TOF • Neutral pions from EMCAL • Charged pions from RICH+EMCAL Cronin effect gone at pT ~ 8 GeV/c

  22. Does Cronin enhancement saturate? • A different approach: • Intrinsic momentum broadening in the excited projectile proton: • hpA: average number of collisions: X.N.Wang, Phys.Rev.C 61 (2000): no upper limit. Zhang, Fai, Papp, Barnafoldi & Levai, Phys.Rev.C 65 (2002): n=4 due to proton d dissociation.

  23. CARTOON flow+jet flow N F Jet physics in PHENIX trigger Trigger: hadron with pT > 2.5 GeV/c Count associated particles for each trigger at lower pT (> 1 GeV/c) • “conditional yield” Near side yield: number of jet associated particles from same jet in specified pT bin Away side yield: jet fragments from opposing jet Intra-jet pairs angular width : N |jTy| Inter-jet pairs angular width : F |jTy|  |kTy| “near side”  < 90° jet partner “away side”  > 90° opposing jet

  24. Questions we can ask • What is the intrinsic (primordial) parton transverse momentum kT? • In a nucleon? Nucleus? • Defines baseline for modifications • What is the fragmentation function? • Shape & width, defined by jT, in p+p collisions • Flavor composition of fragments, to compare observed baryon/meson yields in Au+Au • vital for understanding of mechanism of parton interaction with QCD medium formed at RHIC

  25. jet fragmentation and  momentum |ky| = mean effective transverse momentum of the two colliding partons in the plane  to beam axis |jy| = mean transverse momentum of the hadron with respect to the jet axis (in the plane  to beam axis)

  26. pp and dAu correlation functions 1<pT<1.5 2.2<pT<6.0 p+p h+- correl. Near angle peak Far angle peak d+Au : 5<pT <16 GeV/c assoc. with h+- Fit = const + Gauss(0)+Gauss()

  27. from jet correlations in pp at s = 200GeV PHENIX preliminary |jTy| = 36715 MeV/c z  |kTy| = 66050 MeV/c |kTy| = 920100 MeV/c PHENIX preliminary

  28. Jet cone “width” independent of s * *Subject to same trigger bias by selecting pT of particles CCOR Collaboration Phys. Lett. 97B(1980)163

  29. (2.5<pTtrigg<4.0)@ (1.0<pTtrigg<2.5) flow+jet flow N F Near-side width is constant. Away-side width increases with centrality. Au+Au: lost energy is absorbed by medium

  30. 90° yield Au+Au conditional yields (Number of particle pairs per trigger particle in AuAu) The near-side width is independent of centrality. The away-side width is a strong function of centrality. But if we integrate the entire Gaussian for the away-side, the away-side associated yields change in step with the near side associated yields as they increase with centrality.

  31. R. Fries, et al pQCD spectrum shifted by 2.2 GeV Hydro. expansion at low pT + jet quenching at high pT: Recombination of boosted q’s? Modified fragmentation function INSIDE the medium? Teff = 350 MeV central Au+Au is very baryon rich! nucl-ex/0305036 (PRL) p/ ~1 at high pT in central collisions Higher than in p+p or jets in e+e- collisions

  32. central peripheral Do the baryons scale with Ncoll? Au+Au Baryons appear not suppresed  Ncoll at pT = 2 – 4 GeV/c Yield depends on quark content! Quark recombination…

  33. So, are the baryons soft, or from jets? • Look for jet-like correlations with baryons of pT = 2.5 - 4 GeV/c Identify trigger particle Count associated particles per trigger • If baryon excess from quark recombination (coalescence) Expect fewer jet-like associated particles thermal partons coalescence  no partner So yield of associated particles should decrease when coalescence contribution increases with centrality.

  34. jet partner equally likely for trigger baryons & mesons • slight decrease of baryon associated particles with centrality! • expected from recombination The data say: QM04 consensus: coalescence of jet + thermal partons this is medium modification of the jet fragmentation!

  35. Identify Triggers: Away Side Yields In agreement with other measurements of suppression/broadening Baryon trigger: more associated particles on far side?

  36. Deconfinement? Does colored medium screen c+cbar? 0-20% most central Ncoll=779 40-90% least central Ncoll=45 20-40% semi central Ncoll=296 Look at J/Y nucl-ex/0305030 R.L. Thews, M. Schroedter, J. Rafelski Phys. Rev. C63 054905 (2001): Plasma coalesence model for T=400MeV and ycharm=1.0,2.0, 3.0 and 4.0. L. Grandchamp, R. RappNucl. Phys. A&09, 415 (2002) and Phys. Lett. B 523, 50 (2001): Nuclear Absorption+ absoption in a high temperature quark gluon plasma A. Andronic et. Al. Nucl-th/0303036 Proton EXTRA (thermal) J/Y: no Deconfinement:?J/Y above Tc:??

  37. Open charm: baseline is p+p collisions PHENIX PRELIMINARY Measure charm s via semi-leptonic decay to e+ & e- p0, h, photon conversions are measured and subtracted fit p+p data to get the baseline for d+Au and Au+Au.

  38. No large suppression as for light quarks! PHENIX PRELIMINARY Curves are the p+p fit, scaled by the number of binary collisions

  39. No CGC signal at mid-rapidity So, perhaps Rda G-sat. Rda pQCD >2 BFKL, DGLAP Xc(A) RHIC Pt (GeV/c) Pt (GeV/c) Log Q2 How about Color Glass Condensate? Central: Enhanced not suppressed PHENIX preliminary y=0 Peripheral d+Au (like p+p)

  40. d Au PhenixPreliminary But at forward rapidity reach smaller x y = 3.2 in deuteron direction  x  10-3 in Au nucleus Strong shadowing, maybe even saturation?

  41. h Analysis Photon cuts: - low energy threshold - |TOF| - 2 (photon-like cluster) - fiducial cut Asymmetry cut < 0.5

  42. Yields (shown in arbitrary units)as a function of pT • Yields in 3 centrality selections • 0-20%, 20-60%, 60-92% • Corrected for acceptance, efficiency, and branching ratio • Absolute normalization still being finalized (to present h/p0) • Errors dominated by uncertainty in peak extraction (point-to-point systematic error) PHENIX Preliminary

  43. p0 h Nuclear Modification Factor for h (compared to p0) PHENIX Preliminary RCP =

  44. Statistically it’s a 4 effect Systematic Error under study Efficiency being evaluated Nobody scrambles quarks like we do! Anti-Penta Quarks with PHENIX? Q- n + K- 1.54 GeV

  45. conclusions • Rapid equilibration! • Strong pressure gradients, hydrodynamics works • Constituent scattering cross section is very large • EOS is not hadronic • The hot matter is “sticky” – it absorbs energy & seems to • transport it efficiently • Seeenergy loss/jet quenching • d+Au data says: final state, not initial state effect • So, the stuff is dense, hot, ~ equilibrated AND NEW! • QGP discovery? • J/Y suppression or not? This run • Tinitial? direct photons & low-mass continuum dileptons

  46. “near side” Df < 90° jet partner identified “away side” Df > 90° opposing jet fragment identified Identified Associated Particles--AuAu Trigger (not identified) Perhaps due to PHENIX’s limited  acceptance

  47. Medium properties • Extract by constraining QCD-inspired models with measured jet suppression and v2 • Find (values from Vitev, et al; others consistent)

  48. Implications of the results for QGP • Ample evidence for equilibration • v2 & jet quenching measurements constrain initial gluon density, energy density, and energy loss • parton interaction cross sections 50x perturbative s • parton correlations at T>Tc • complicates cc bound states as deconfinement probes! • Hadronization by coalescence of thermal,flowing quarks • v2 & baryon abundances point to quark recombination as hadronization mechanism • Jet data imply must also include recombination between quarks fromjets and the thermalized medium •  medium modifies jet fragmentation!

  49. J/y in pp and d+Au • Total cross section : BR pp = 159 nb ± 8.5 % (fit) ± 12.3% (abs)

  50. dAu/pp versus rapidity

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