1 / 60

Relativistic Heavy Ion Physics: An Experimental Review

Relativistic Heavy Ion Physics: An Experimental Review. Saskia Mioduszewski. 22 July 2003. Outline. Physics Goals: deconfinement and chiral symmetry restoration Overview of the Program Global Observables charged-particle multiplicity flow Other Experimental Highlights J/ y suppression

alena
Download Presentation

Relativistic Heavy Ion Physics: An Experimental Review

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Relativistic Heavy Ion Physics: An Experimental Review Saskia Mioduszewski 22 July 2003

  2. Outline • Physics Goals: deconfinement and chiral symmetry restoration • Overview of the Program • Global Observables • charged-particle multiplicity • flow • Other Experimental Highlights • J/y suppression • low mass dilepton enhancement • high pT suppression • Summary

  3. Lattice QCD at Finite Temperature • Coincident transitions: deconfinement and chiral symmetry restoration Ideal gas(Stefan-Boltzmann limit) F. Karsch, hep-ph/010314 (mB=0) Critical energy density: Chiral symmetry spontaneously broken in nature. Quark condensate is non-zero: At high temperature and/or baryon density Constituent mass  current mass Chiral Symmetry (approximately) restored. TC ~ 175 MeV  eC ~ 0.7 GeV/fm3

  4. early universe P. Braun-Munzinger, nucl-ex/0007021 250 RHIC quark-gluon plasma 200 Temperature T [MeV] SPS AGS Lattice QCD deconfinement chiral restoration 150 thermal freeze-out SIS 100 hadron gas neutron stars atomic nuclei 50 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] 0 Schematic Phase Diagram of Strongly Interacting Matter Test QCD under extreme conditions and in large scale systems Search for deconfined QGP phase SISAGS  SPS RHICLHC From high baryon density regime to high temperature regime

  5. How to Observe QGP in Heavy Ion Collisions Some tools to distinguish QGPfromdense hadron gas: • Direct observation of deconfinement: suppression of J/ • High energy density: interaction of jets with medium • High temperature: direct photons/dileptons • Chiral symmetry restoration: meson properties (m,) expected to be modified in medium • Equilibration at early stage large pressure collective expansion: flow

  6. History of High-Energy A+B Beams • BNL-AGS: mid 80’s, early 90’s O+A, Si+A 15 AGeV/c sNN ~ 6 GeV Au+A 11 AGeV/c sNN ~ 5 GeV • CERN-SPS: mid 80’s, 90’s O+A, S+A 200 AGeV/c sNN ~ 20 GeV Pb+A 160 AGeV/c sNN ~ 17 GeV • BNL-RHIC: early 00’s Au+Au sNN ~ 130 GeV Au+Au, p+p, d+Au sNN ~ 200 GeV

  7. STAR The RHIC Experiments

  8. Global Observables Reflect the conditions of the system after freeze-out, after resonance decays • Charged-Particle Multiplicity • helps constrain models • reflects produced entropy • Flow • collective expansion, rescattering • pressure

  9. Spectators 100% 0 % Participants Spectators AA collisions are not all the same Nuclei are extended objects • Impact parameter • Number of participants • Centrality ( % from total inelastic cross-section)

  10. NA49 dn/dy h- BRAHMS (0-5%): Nch (||<4.7) = 3860 ± 300 NA49 (0-5%): Nh-(|y| < 3) = 695 ± 30 - Factor of  3 more particles produced at RHIC than at SPS - Wider  distribution Charged-Particle Rapidity Distribution RHIC BRAHMS SPS • Enhancement of particle production for central collisions at mid-rapidity. • Particle production scales with Npart at high rapidities (h >3).

  11. RHIC SPS AGS ÖsNN Dependence of dNch/dy  From SPS to RHIC : * dNch/dy increases by ~70% atÖsNN = 130 GeV * dNch/dy increases by ~90% at ÖsNN = 200 GeV • ln(ÖsNN)dependence from AGS to RHIC

  12. Radial Flow – Expansion of system due to pressure – Heavier particles shifted to higher pT – Observable: <bT> from slopes of mT spectra as a function of mass – Spectra can be described by hydrodynamic models for pT< 2-3 GeV/c and mid-peripheral to central events

  13. Single Particle Spectra (low pT) • Decreasing slope for increasing particle mass and centrality T. Ullrich QM2002

  14. Single Particle Spectra for most central events (0-5%) J. Burward-Hoy, QM2002 PHENIX Preliminary PHENIX Preliminary Au+Au at sqrt(sNN) =200GeV Au+Au at sqrt(sNN) =200GeV • proton yield ~ pion yield @ 2 GeV • consistent with hydrodynamic model calculations (e.g. comparison to 130 GeV data -Teaney, Lauret, Shuryak nucl-th/0110037)

  15. Mean Transverse Momentum vs. Npart J. Burward-Hoy, QM2002 closed symbols: 200 GeV open symbols: 130 GeV <pT> increases with Npart and particle mass, indicative of radial expansion Relative increase with Npart greater for (anti)p than for , K

  16. Hydrodynamic Model Fit to the Spectra J. Burward-Hoy, QM2002 Most central collisions for 200 GeV data PHENIX: Freeze-out Temperature Tfo = 110  23 MeV Transverse flow velocity bT = 0.7  0.2  < bT>~ 0.5 Au+Au at sqrt(sNN) =200GeV Ref: E. Schnedermann, J. Sollfrank, and U. Heinz, Phys. Rev. C 48, 2462 (1993) STAR: Tfo ~ 100 MeV bT ~ 0.6

  17. Mid-Rapidity mT spectra at SPS M. van Leeuwen QM2002 (NA49) NA57, H. Helstrup, this conference: Tfo = 131 ± 10 MeV <bT> = 0.47 ± 0.02

  18. Momentum space: final asymmetry Coordinate space: initial asymmetry py multiple collisions (pressure) px Elliptic Flow in Non-central Collisions • Early state manifestation of collective behavior: • Asymmetry generated early in collision, quenched by expansion  observed asymmetry emphasizes early time Second Fourier coefficient v2:

  19. Elliptic Flow • Strongelliptic flow signal   strong (collective) pressure • Largeandfast rescattering(early thermalization) • v2 dependent on mass (predicted by hydro P. Huovinen et al, PLB 503 (2001) 58).

  20. Elliptic Flow 130 GeV data Wetzler QM2002 • SPS: v2 ~ 0.03 • RHIC: v2 ~ 0.055 E877: Phys.Lett.B474:27-32, 2000 CERES: QM2001 INPC 2001 nucl-ex/0109017 STAR: PRC66 (2002) 034904 NA49 Preliminary

  21. Flow: Comparison of SPS and RHIC • Radial Flow: pressure can build up over entire dynamics • <bT> ~ 0.4 - 0.5 at SPS • <bT> ~ 0.5 - 0.6 at RHIC • Elliptic Flow: pressure must build up before asymmetry of system has diminished • v2 ~ 0.03 at SPS • v2 ~ 0.06 at RHIC • Moderate increase in <bT>  more pressure at RHIC • Significantly larger v2 is evidence for early build-up of pressure • According to hydrodynamic models  early thermalization at RHIC (t~0.6fm/c -Heinz, Kolb Nucl.Phys.A702:269-280,2002)

  22. Energy Density Energy density a la Bjorken: Estimate e for RHIC: dET/dy ~ 720 GeV(S. Bazilevsky QM2002, PHENIX PRELIMINARY)

  23. Other Highlights of Program • Global observables  properties of collision dynamics, EOS • Other probes for signatures of QGP • J/y suppression  deconfinement • low mass dileptons  chiral symmetry restoration • high pT suppression  density of produced medium and energy loss

  24. J/y suppression: probe of deconfinement • An “old” signature of QGP formation: (Matsui and Satz PL B178, (1986) 416). • At high enough color density, the screening radius < binding radius  J/ will dissolve • Observation: Anomalous suppression in Pb-Pb collisions * beyond normal nuclear absorptionabs ~ 4-6 mb

  25. J/y suppression: Evidence of deconfinement? NA50 Preliminary L. Ramello, QM 2002 Suppression increasing with centrality (discontinuities?) Exceeds normal nuclear absorption (as measured in p+A) Many models exist (hadronic and QGP) – data consistent with suggested QGP signature (Matsui, Satz, Kharzeev)

  26. Charmonium (J/Y) physicsat RHIC • possible signature of the deconfinement phase transition • J/Y yield can be • suppressed more than at SPS - dissolve in QGP (longer lifetime, higher temperature than SPS) • enhanced - cc coalescence as the medium cools (2 orders of magnitude more production of cc pairs at RHIC) • important to measure J/Y in p+p and d+Au to separate “normal” nuclear effects • shadowing • nuclear absorption in cold matter • J/Y measurements in leptonic decay channels • J/Y e+ e- and J/Y m+ m-in p+p at s = 200 GeV • J/Y e+ e-in Au+Au at sNN = 200 GeV (hep-ex/0307019) (nucl-ex/0305030)

  27. normal nuclear absorption: Pb+Pb at CERN SPS (NA50) J/Y Production at RHIC PHENIX, sNN = 200 GeV • J/Y-Suppression maybe most compelling QGP evidence at CERN SPS • Expectation at RHIC energies unclear 10 cc pairs produced per central Au+Au collision • Possibly enhanced J/Y- production due to charm-coalescence - PLB477(2000) 28 normalized to PHENIX p+p measurement

  28. Dy = 1.0 coalescence model (Thews at al.) Dy = 4.0 statistical model (Andronic at al.) absorption model (Grandchamp et al.) Model comparisons • models that predict enhancement relative to binary collision scaling are disfavored • no discrimination between models that lead to suppression

  29. No enhancement in pp and pA collisions Low-Mass e+e- pairs Main CERES Result: Strong enhancement of low-mass pairs in A-A collisions (wrt to expected yield from known sources) Enhancement factor (.25 <m<.7GeV/c2): 2.6 ± 0.5 (stat) ± 0.6 (syst)

  30. -meson broadening Dropping -meson mass  scattering off baryons(Rapp, Wambach et al) (G.E. Brown et al) Interpretations Add  annihilation: +-  * e+e- (thermal radiation from HG) Cross section dominated by pole at the  mass of the  em form factor: Plus or

  31. d.o.f. hadrons quarks Onset of Chiral Symmetry Restoration? In-medium -meson broadening Dropping -meson mass (Rapp, Wambach et al) (G.E. Brown et al) What happens as chiral symmetry is restored? Dropping mass or broadening (melting)?

  32. schematic view of jet production leading particle hadrons q q hadrons leading particle Fate of Hard Scattered Partons in Au+Au Collisions • Hard scatterings in nucleon-nucleon collisions produce jets of particles. • In the presence of a color-deconfined medium, the partons strongly interact (~GeV/fm) losing much of their energy. • “Jet Quenching”

  33. Nuclear Modification Factor RAA • in absence of nuclear effects • RAA < 1 at low pT (soft physics regime) • RAA = 1 at high pT (hard scattering regime) • “suppression” (enhancement, e.g. Cronin effect) • RAA < 1 (> 1) at high pT Nuclear Modification Factor <Nbinary>/sinelp+p NN cross section

  34. RAA for p0 By definition, processes that scale with Nbinarywill produce RAA=1. RAA is what we measure divided by what we expect. Nbinary-scaling RAA is < 1 at RHIC, but > 1 at SPS SPS: “Cronin” effect dominates RHIC: suppression dominates A.L.S.Angelis PLB 185, 213 (1987) WA98, EPJ C 23, 225 (2002) PHENIX, PRL 88 022301 (2002) PHENIX submitted to PRL, nucl-ex/0304022

  35. comparison with model calculations with and without parton energy loss Levai without parton energy loss Wang Wang with parton energy loss Vitev Levai Jet Quenching ? • high pT suppression reproduced by models with parton energy loss • other explanations not ruled out, need to measure initial-state effects Wang: X.N. Wang, Phys. Rev. C61, 064910 (2000). Levai:P.Levai, Nuclear Physics A698 (2002) 631. Vitev: I. Vitev and M. Gyulassy, hep-ph/0208108 + Gyulassy, Levai,Vitev, Nucl. Phys. B 594, p. 371 (2001). Au+Aup0+X at sNN = 200 GeV

  36. - Consistent observation by all 4 experiments in charged hadron measurement • RAA is well below 1 for both charged hadrons and neutral pions. • The neutral pions fall below the charged hadrons since they do not contain contributions from protons and kaons (will be discussed later). Strong Suppression! BRAHMS, Z. Yin, this conference PHOBOS, R. Nouicer, this conference RAA for p0 and charged hadrons PHENIX AuAu 200 GeV p0 data: nucl-ex/0304022, submitted to PRL. charged hadron (preliminary) : NPA715, 769c (2003).

  37. Au+Au peripheral Au+Au central pedestal and flow subtracted ? Phys Rev Lett 90, 082302 Azimuthal distributions in Au+Au Near-side: peripheral and central Au+Au similar to p+p Strong suppression of back-to-back correlations in central Au+Au collisions

  38. BRAHMS, Z. Yin, this conference PHOBOS, R. Nouicer, this conference d+Au Au+Au RAA vs. RdA for charged hadrons and p0 Initial State Effects Only PHENIX (d+Au) hep-ex/0306021 submitted to PRL Initial + Final State Effects No Suppression in d+Au, instead small enhancement observed (Cronin effect)!! d-Au results rule out initial-state effects as the explanation for Suppression at Central Rapidity and high pT

  39. pedestal and flow subtracted Azimuthal distributions Near-side: p+p, d+Au, Au+Au similar Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au Suppression of the back-to-back correlation in central Au+Au is a final-state effect

  40. High pT Measurements at RHIC d+Au collisions: • No suppression at high pT • Away-side jet strength consistent with p+p collisions Peripheral Au+Au collisions: • Hadron yields consistent with Nbinary-scaled yields in p+p collisions • Away-side jet strength consistent with p+p collisions Central Au+Au collisions: • Hadrons are suppressed at high pT (up to 10 GeV/c) • Away-side jet disappears Particle Composition in Central Au+Au collisions: What is happening with the protons?

  41. PHENIX, nucl-ex/0305036 Particle Species Dependence of High pT Suppression No apparent proton suppression for 2-4 GeV/c • different production mechanism ? (Similar effect seen in STAR for  vs. Kshort suppression)

  42. Particle Composition at High pT • p/p < 0.25 expected from jet fragmentation • observed p/p ~ 0.4 in peripheral, ~ 1 in central • protons from non-fragmentation sources ? nucl-ex/0305036

  43. Summary Physics highlights: • Strong collective expansion at SPS and RHIC • Evidence for early equilibration at RHIC • SPS: * Anomalous J/ suppression * Enhancement of low-mass dileptons • RHIC: * Suppression of high pT particles and disappearance of away-side jet Very intriguing results. All consistent with QGP formation

  44. Extra Slides

  45. Direct Photons (I) WA98 • Evidence for direct photons in • central Pb-Pb collisions? • 10-20% excess but 1 effect only • CERES preliminary result: • enhancement = • 12.4% ± 0.8% (stat) ± 13.5% (syst)

  46. WA98 Srivastava and Sinha nucl-th/0006018 Hydro calculations : Prompt + QGP  Mixed phase  HG QGP dominates at high pT Direct Photons (II) • Comparison to scaled pA: similar spectrum • but factor of ~2 enhanced yield in Pb-Pb, • again ~1 effect. • pQCD underpredicts direct photon yield

  47. Direct Photons pQCD calculation for direct g and p0 in p+p at s=200 GeV (Werner Vogelsang): Direct Photons: • Photons not originating from hadron decays like p0gg • gall = gdirect+ gdecay • Direct photon signal seen in Pb+Pb at sNN=17.3 GeV • Stronger signal expected at RHIC, because • p0 suppressed by factor 5 • Suppression appears to be a final state effect • Direct photons not affected by final state interactions

  48. preliminary preliminary preliminary Direct Photon Search • Au+Au at sNN = 200 GeV • No direct photon signal seen within errors • With further analysis systematic errors will be reduced ...

  49. STAR Azimuthal asymmtery (v2) at high pT Finite v2 up pT ~ 10 GeV Hydrodynamics up to pT ~ 2-3 GeV Jets correlated to reaction plane?

  50. Neutral Pion Production in central and peripheral Au+Au collisions • reference p+p data with same detector • binary scaling in peripheral Au+Au • suppression factor ~ 5 in central Au+Au Binary scaling ×1/5 Participant scaling p0 at sNN = 200 GeV nucl-ex/0304022, submitted to PRL

More Related