1 / 51

The Quark-Gluon Plasma Comes of Age

The Quark-Gluon Plasma Comes of Age. Peter Jacobs, Lawrence Berkeley National Laboratory. Outline. Brief tour of QCD QCD Matter and its phase transitions Quantitative measurements of QCD Matter: jet quenching and shear viscosity

camdyn
Download Presentation

The Quark-Gluon Plasma Comes of Age

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. The Quark-Gluon Plasma Comes of Age Peter Jacobs, Lawrence Berkeley National Laboratory The QGP comes of age

  2. Outline • Brief tour of QCD • QCD Matter and its phase transitions • Quantitative measurements of QCD Matter: jet quenching and shear viscosity • What’s the deal with string theory and heavy ion collisions? • Future directions at RHIC and the LHC The QGP comes of age

  3. Quantum Chromodynamics (QCD) The Strong Interaction in the Standard Model W, Z boson:Weak interaction Leptons • (photon): EM interaction Quarks g (gluon):Strong interaction strong coupling constant The QGP comes of age

  4. Q2 Running of the coupling in relativistic field theory Small momentum transfer Q2 large distance scales Large momentum transfer Q2 small distance scales Virtual pairs (loops) screen bare interaction  momentum-dependent interaction strength The QGP comes of age

  5. Running of the coupling: QED vs QCD negative QED: • Larger |Q2| (smaller distance)  larger coupling • similar to screening of charge in di-electric material QCD: =+(33-12)/12p = positive! Larger |Q2| (smaller distance)  smaller coupling And that makes a huge difference! The QGP comes of age

  6. Asymptotic Freedom Confinement Gross Politzer Wilczek 0.2 fm 0.02 fm 0.002 fm Running of aS The QGP comes of age

  7. Deep inelastic scattering small x x = partonic momentum fraction large x QCD is a precise theory at large Q2 Inclusive jet production The QGP comes of age

  8. Pressure Phase Diagram of Water Not directly calculable from the QED Lagrangian: complex emergentfeatures The QGP comes of age

  9. Phase Diagram of QCD Matter high T ~ high Q2 ~ deconfinement The QGP comes of age

  10. Early Universe • COBE and WMAP: universe is highly equilibrated •  relics of early phase transitions are difficult to see The QGP comes of age

  11. Lattice QCD at Finite Temperature Ideal gas (Stefan-Boltzmann limit) Not an ideal gas even at 3TC (will return to this point) F. Karsch, hep-ph/0103314 Critical energy density: TC ~ 175 MeV  eC ~ 1 GeV/fm3 The QGP comes of age

  12. STAR The Relativistic Heavy Ion Collider The QGP comes of age

  13. Calibrated in p+p and p/d+A Calculable final state medium effects (pQCD-based) Hard probes of QCD matter • Calculable interactions of energetic partonswith the medium •  calibrated, penetrating tomographic probes The QGP comes of age

  14. B.I. Abelev et al., PRL 97, 252001 (2006) p0 Testing pQCD in p+p at RHIC Inclusive jets • Good agreement with NLO pQCD •  pQCD should be broadly applicable The QGP comes of age

  15. p0 Binary collision scaling p+p reference Jet quenching: hadron suppression Energy loss  softening of fragmentation  suppression of leading hadron yield The QGP comes of age

  16. Photons (color-neutral) Jets (color-charged) Jet quenching I: hadrons are suppressed, photons are not The QGP comes of age

  17. trigger Jet structure via hadron correlations p+p  dijet Full jet reconstruction in the heavy ion environment is difficult  probe jet structure via dihadron correlations Phys Rev Lett 90, 082302 The QGP comes of age

  18. trigger ? recoil Hard recoil hadrons All recoil hadrons pTassoc > 0.15 GeV cos(Df) pTassoc > 2 GeV STAR, Phys Rev Lett 91, 072304 STAR, Phys Rev Lett 95, 152301 Jet quenching II: recoiling jets are strongly modified 4< pTtrig < 6 GeV Striking qualitative effects: conclusive evidence for large partonic energy loss in dense matter The QGP comes of age

  19. Transport coefficient: Radiative energy loss in QCD Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000) BDMPS model: multiple soft collisions in a medium of static color charges Medium-induced gluon radiation spectrum: Total medium-induced energy loss: DE independent of parton energy (finite kinematics DE~log(E)) DE  L2 due to interference effects (expanding medium DE~L) The QGP comes of age

  20. Eskola et al ‘04 qhat from single hadron suppression The QGP comes of age

  21. ~RHIC data Hadronic matter Deconfined matter  R. Baier, Nucl Phys A715, 209c What does measure? • Equilibrated gluon gas: • number density ~T3 • energy density e~T4 qhat+modelling  energy density Model uncertainties • pQCD result: c~2 (aS? quark dof? …) • sQGP (multiplicities+hydro): c~10 The QGP comes of age

  22. Eskola et al. ‘04 ? • Core of fireball is opaque to jets •  RAA provides onlypoor upper constraint on The limitations of hadron suppression Look for more sensitive observables… The QGP comes of age

  23. trigger Yield per trigger pTtrigger>8 GeV/c ? recoil STAR, nucl-ex/0604018 Dihadron correlations at higher pT Recoil jet clearly seen above background but at suppressed rate differential measurement of`DE  upper bound on qhat The QGP comes of age

  24. Trigger direction STAR preliminary Df High pT hadrons: detailed dynamical calculations T. Renk, hep-ph/0602045 Different geometrical biases underly trigger and recoil distributions ~75% of recoils due to non-interacting jets All bremsstrahlung models: discrete term The QGP comes of age

  25. Zhang, Owens, Wang and Wang nucl-th/0701045 Df from single and di-hadon suppression Consistent minima for two independent measurements The QGP comes of age

  26. QCD Matter at T~200 MeV: Main new result in this talk: the first accurate* measurement of a transport property of QCD Matter * excluding theoretical uncertainties The QGP comes of age

  27. Testing radiative energy loss: heavy quarks Q • In vacuum, gluon radiation suppressed at q < mQ/EQ • “dead cone” effect: b, c quarks fragment hard into heavy mesons Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602. Dokshitzer and Kharzeev, PLB 519 (2001) 199. Dead cone also implies lower heavy quark energy lossin matter: radiation cannot outrun the probe(Dokshitzer-Kharzeev, 2001)  heirarchy of jet energy loss: gluon > u,d,s > charm > bottom The QGP comes of age

  28. Standard radiative energy loss ignore b-quark contribution Heavy quark suppression via b,c→e+X Heavy quarks are “over-suppressed” missing mechanisms? Energy loss via elastic scattering? The QGP comes of age

  29. inner trackers for PHENIX and STAR Heavy quark suppression cont’d Validation of radiative energy loss theory requires resolution of heavy quark suppression puzzle Need new detectors to explicitly separate b and c contributions: important Kent State contributions… The QGP comes of age

  30. z y x Collective Flow of QCD Matter py px Final momentum anisotropy Reaction plane defined by “soft” (low pT) particles Initial spatial anisotropy Elliptic flow The QGP comes of age

  31. Light particles Heavy particles Good agreement requires thermalization at time Relativistic (Perfect) Hydrodynamics Heinz ‘04 Mass hierarchy vs momentum is characteristic of common velocity distribution The QGP comes of age

  32. Shear viscosity in fluids • Properties are counter-intuitive: • Weak coupling • small cross section, long mean free path •  large viscosity • Strong coupling • large cross section, small mean free path •  small viscosity h→0: strongly coupled (perfect) fluid h→: weakly coupled (ideal) gas (!) The QGP comes of age

  33. vary initial matter distribution Teaney ‘03 finite h T. Hirano et al., nucl-th/0701075 Constraint on shear viscosity: How perfect a fluid is QCD Matter?  finite h not excluded Qualitatively, h is “small” Quantitative measurement requires more detailed modeling and data The QGP comes of age

  34. Maldacena ’98: high temperature strongly-coupled gauge theory in 3+1 dimensions classical string theory in vicinity of black hole in 4+1 dimensions Black holes and gauge theory via theAdS/CFT correspondence Warning: I am not a string theorist. Conjecture: hidden within every non-Abelian gauge theory, even within the weak and strong nuclear interactions, is a theory of quantum gravity.(Horowitz and Polchinski, gr-qc/0602037 ) The QGP comes of age

  35. Shear visc. ~ cross section: Beckenstein entropy: Shear viscosity and entropy in AdS/CFT h/s of a black hole (M. Natsuume, hep-ph/0700120) Compare RHIC elliptic flow+hydro: h/s~0.1 Universal result: gauge theory plasmas with gravity duals have a universal low value of h/s at strong (‘t Hooft) coupling Kovtun, Son and Starinets (KSS), PRL 94, 111601 The QGP comes of age

  36. Spectral Properties of Hot QCD Nakamura & Sakai, hep-lat/0510100 h/s pQCD AdS/CFT T/Tc Shear viscosity: Lattice QCD vs AdS/CFT Lattice: quenched approximation (no quarks) Numerical agreement! The QGP comes of age

  37. Can also calculate dynamical processes… Heavy quark is end of string on boundary Hot gauge theory lives on boundary String provides drag (energy loss) Black-hole horizon Friess et al., hep-th/0607022 Jet quenching in AdS/CFT The QGP comes of age

  38. Recall Jet quenching: pQCD vs AdS/CFT Weak-coupling pQCD (Baier et al.): Proportional to NC2 ~ entropy density Strong-coupling N=4 SYM (Liu, Rjagopal and Wiedemann): NOT proportional to NC2 ~ entropy density Rough numerical agreement The QGP comes of age

  39. String theory and hot QCD: comments • At first sight the string theory connection looks unlikely to succeed.The gauge theories that have known gravity duals are not QCD: • wrong degrees of freedom, infinite number of colors • supersymmetric • strong coupling limit • conformal theory (no running of the coupling) • no confinement or chiral symmetry • But some of these can be relaxed towards QCD (e.g. d.o.f, conformality) • But also, analogy to condensed matter physics: metals have widely differing structure yet have essential common features • The AdS/CFT correspondence may teach us about the emergent features of QCD-like theories • (thermodynamics, transport properties,…) The QGP comes of age

  40. String Theory summary cont’d • The definitive connection of gauge theories to black hole physics would be a development of the first rank in importance! • Numerical agreements with data and Lattice QCD are provocative but not proofs of validity • For rigorous science need hard, testable predictions: • e.g. momentum dependence of J/ suppression (Liu, Rajagopal, Wiedemann) • Stay tuned! The QGP comes of age

  41. The New Yorker, Jan. 7 2007 The QGP comes of age

  42. Large Hadron Collider at CERN mid-late 2007: commission 14 TeV p+p end 2008: first long 5.5 TeV Pb+Pb run heavy ion running: 4 physics weeks/year CMS ATLAS ALICE The QGP comes of age

  43. P. Jacobs and M. van Leeuwen Nucl. Phys A774, 237 (2006) Jet quenching at the LHC • Pb+Pb at 5.5 TeV: • First ion collisions 2008 • qualitatively new probes •  enormous reach in jet energy The QGP comes of age

  44. B.I. Abelev et al., PRL 97, 252001 (2006) Jets and hadrons at RHIC II RHIC II (x 10 luminosity upgrade): also has significant kinematic reach (jets to ~60-70 GeV) The QGP comes of age

  45. What is interesting about high ET jetsat RHIC II and LHC? Precision QCD: the evolution of nucleon structure with Q2 (= resolution of the probe) High ET jets at LHC and RHIC may provide similarly precise probes of hot QCD matter The QGP comes of age

  46. ALICE TOF TRD HMPID EMCal ITS PMD Muon Arm PHOS Size: 16 x 26 meters Weight: 10,000 tons TPC The QGP comes of age

  47. The QGP comes of age

  48. U.S. Contribution to ALICE: EMCal a large electromagnetic calorimeter Enables jet measurements in ALICE • Approved by LHCC 9/28/06 • 10+1/2+1/2=11 super-modules • 8 SM from US • 3 SM from France, Italy US Total Project Cost: $13.3M CD-2/3 expected summer ‘07 The QGP comes of age

  49. Jet quenching pThadron~2 GeV =ln(EJet/phadron) Benchmark observable: modified fragmentation function • MLLA: good description of vacuum fragmentation (basis of PYTHIA) • introduce medium effects at parton splitting Borghini and Wiedemann, hep-ph/0506218 Jet quenching  fragmentation strongly modified at pThadron~1-5 GeV The QGP comes of age

  50. ALICE+EMCal in one LHC year Detailed measurements of change in jet structure due to energy loss Large jet quenching effects, exquisite statistical sensitivity The key physics issue: how does this distribution evolve with Q2 (ET)? The QGP comes of age

More Related