Kent State University, March 8, The QGP comes of age The Quark-Gluon Plasma Comes of Age Peter Jacobs, Lawrence Berkeley National Laboratory

Kent State University, March 8, The QGP comes of age 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 Outline

Kent State University, March 8, The QGP comes of age Quantum Chromodynamics (QCD) The Strong Interaction in the Standard Model Quarks Leptons g (gluon):Strong interaction W, Z boson:Weak interaction  (photon): EM interaction strong coupling constant

Kent State University, March 8, The QGP comes of age Running of the coupling in relativistic field theory Q2Q2 Small momentum transfer Q 2  large distance scales Large momentum transfer Q 2  small distance scales Virtual pairs (loops) screen bare interaction  momentum-dependent interaction strength

Kent State University, March 8, The QGP comes of age Running of the coupling: QED vs QCD Larger |Q 2 | (smaller distance)  larger coupling similar to screening of charge in di-electric material QED: negative QCD:QCD: =+(33-12)/12  = positive! Larger |Q 2 | (smaller distance)  smaller coupling And that makes a huge difference!

Kent State University, March 8, The QGP comes of age Running of  S 0.2 fm0.02 fm0.002 fm ConfinementAsymptotic Freedom Gross Politzer Wilczek

Kent State University, March 8, The QGP comes of age QCD is a precise theory at large Q 2 Inclusive jet production Deep inelastic scattering small x large x x = partonic momentum fraction

Kent State University, March 8, The QGP comes of age Phase Diagram of Water Not directly calculable from the QED Lagrangian: complex emergent features Pressure

Kent State University, March 8, The QGP comes of age Phase Diagram of QCD Matter high T ~ high Q 2 ~ deconfinement

Kent State University, March 8, The QGP comes of age Early Universe COBE and WMAP: universe is highly equilibrated  relics of early phase transitions are difficult to see

Kent State University, March 8, The QGP comes of age Lattice QCD at Finite Temperature F. Karsch, hep-ph/ Critical energy density: T C ~ 175 MeV  C ~ 1 GeV/fm 3 Ideal gas (Stefan-Boltzmann limit ) Not an ideal gas even at 3T C (will return to this point)

Kent State University, March 8, The QGP comes of age STAR The Relativistic Heavy Ion Collider

Kent State University, March 8, The QGP comes of age Calibrated in p+p and p/d+A Calculable final state medium effects (pQCD-based) Hard probes of QCD matter Calculable interactions of energetic partons with the medium  calibrated, penetrating tomographic probes

Kent State University, March 8, The QGP comes of age Testing pQCD in p+p at RHIC  Good agreement with NLO pQCD  pQCD should be broadly applicable Inclusive jets B.I. Abelev et al., PRL 97, (2006)

Kent State University, March 8, The QGP comes of age  Jet quenching: hadron suppression - Energy loss  softening of fragmentation  suppression of leading hadron yield Binary collision scalingp+p reference

Kent State University, March 8, The QGP comes of age Jet quenching I: hadrons are suppressed, photons are not Jets (color- charged) Photons (color- neutral)

Kent State University, March 8, The QGP comes of age Jet structure via hadron correlations p+p  dijet Full jet reconstruction in the heavy ion environment is difficult  probe jet structure via dihadron correlations trigger Phys Rev Lett 90,

Kent State University, March 8, The QGP comes of age Jet quenching II: recoiling jets are strongly modified 4< p T trig < 6 GeV trigger recoil ? STAR, Phys Rev Lett 91, p T assoc > 2 GeV Hard recoil hadrons cos(  ) p T assoc > 0.15 GeV STAR, Phys Rev Lett 95, All recoil hadrons Striking qualitative effects: conclusive evidence for large partonic energy loss in dense matter

Kent State University, March 8, The QGP comes of age Radiative energy loss in QCD BDMPS model: multiple soft collisions in a medium of static color charges  E independent of parton energy (finite kinematics  E~log(E))  E  L 2 due to interference effects (expanding medium  E~L) Medium-induced gluon radiation spectrum: Total medium-induced energy loss: Transport coefficient: Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000)

Kent State University, March 8, The QGP comes of age qhat from single hadron suppression Eskola et al ‘04

Kent State University, March 8, The QGP comes of age What does measure? Equilibrated gluon gas: number density  ~T 3 energy density  ~T 4  qhat+modelling  energy density pQCD result: c~2 (  S ? quark dof? …) sQGP (multiplicities+hydro): c~10 Model uncertainties R. Baier, Nucl Phys A715, 209c Hadronic matter Deconfined matter ~RHIC data

Kent State University, March 8, The QGP comes of age The limitations of hadron suppression ? Core of fireball is opaque to jets  R AA provides only poor upper constraint on Eskola et al. ‘04 Look for more sensitive observables…

Kent State University, March 8, The QGP comes of age Dihadron correlations at higher p T Recoil jet clearly seen above background but at suppressed rate differential measurement of`  E  upper bound on qhat trigger recoil ? p T trigger >8 GeV/c Yield per trigger STAR, nucl-ex/

Kent State University, March 8, The QGP comes of age  STAR preliminary T. Renk, hep-ph/ High p T hadrons: detailed dynamical calculations Trigger direction Different geometrical biases underly trigger and recoil distributions ~75% of recoils due to non-interacting jets All bremsstrahlung models: discrete term

Kent State University, March 8, The QGP comes of age Zhang, Owens, Wang and Wang nucl-th/ from single and di-hadon suppression  Consistent minima for two independent measurements

Kent State University, March 8, The QGP comes of age Main new result in this talk: the first accurate * measurement of a transport property of QCD Matter QCD Matter at T~200 MeV: * excluding theoretical uncertainties

Kent State University, March 8, The QGP comes of age Testing radiative energy loss: heavy quarks In vacuum, gluon radiation suppressed at  < m Q /E Q “dead cone” effect: b, c quarks fragment hard into heavy mesons Q Dokshitzer, Khoze, Troyan, JPG 17 (1991) Dokshitzer and Kharzeev, PLB 519 (2001) 199. Dead cone also implies lower heavy quark energy loss in matter: radiation cannot outrun the probe (Dokshitzer-Kharzeev, 2001)  heirarchy of jet energy loss: gluon > u,d,s > charm > bottom

Kent State University, March 8, The QGP comes of age Heavy quark suppression via b,c→e+X Standard radiative energy loss ignore b-quark contribution Heavy quarks are “over-suppressed”  missing mechanisms? Energy loss via elastic scattering?

Kent State University, March 8, The QGP comes of age 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: inner trackers for PHENIX and STAR important Kent State contributions…

Kent State University, March 8, The QGP comes of age Collective Flow of QCD Matter x y z Initial spatial anisotropy pypy pxpx Final momentum anisotropy Reaction plane defined by “soft” (low p T ) particles Elliptic flow

Kent State University, March 8, The QGP comes of age Relativistic (Perfect) Hydrodynamics Good agreement requires thermalization at time Heinz ‘04 Mass hierarchy vs momentum is characteristic of common velocity distribution Heavy particles Light particles

Kent State University, March 8, The QGP comes of age 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 Shear viscosity in fluids  →0: strongly coupled (perfect) fluid  →  : weakly coupled (ideal) gas (!)

Kent State University, March 8, The QGP comes of age How perfect a fluid is QCD Matter? Constraint on shear viscosity:  finite  not excluded Qualitatively,  is “small” Quantitative measurement requires more detailed modeling and data Teaney ‘03 T. Hirano et al., nucl-th/ vary initial matter distribution finite 

Kent State University, March 8, The QGP comes of age Black holes and gauge theory via the AdS/CFT correspondence Maldacena ’98: high temperature strongly-coupled gauge theory in 3+1 dimensions classical string theory in vicinity of black hole in 4+1 dimensions 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/ )gr-qc/ Warning: I am not a string theorist.

Kent State University, March 8, The QGP comes of age Shear viscosity and entropy in AdS/CFT  /s of a black hole (M. Natsuume, hep-ph/ ) Universal result: gauge theory plasmas with gravity duals have a universal low value of  /s at strong (‘t Hooft) coupling Kovtun, Son and Starinets (KSS), PRL 94, Compare RHIC elliptic flow+hydro:  /s~0.1 Shear visc. ~ cross section: Beckenstein entropy:

Kent State University, March 8, The QGP comes of age Spectral Properties of Hot QCD Nakamura & Sakai, hep-lat/ T/T c   /s pQCD AdS/CFT Shear viscosity: Lattice QCD vs AdS/CFT Lattice: quenched approximation (no quarks) Numerical agreement!

Kent State University, March 8, The QGP comes of age Jet quenching in AdS/CFT Friess et al., hep-th/ Hot gauge theory lives on boundary Heavy quark is end of string on boundary String provides drag (energy loss) Can also calculate dynamical processes… Black-hole horizon

Kent State University, March 8, The QGP comes of age Jet quenching: pQCD vs AdS/CFT Weak-coupling pQCD (Baier et al.): Strong-coupling  =4 SYM (Liu, Rjagopal and Wiedemann): NOT proportional to N C 2 ~ entropy density Proportional to N C 2 ~ entropy density Recall Rough numerical agreement

Kent State University, March 8, The QGP comes of age 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,…)

Kent State University, March 8, The QGP comes of age 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! String Theory summary cont’d

Kent State University, March 8, The QGP comes of age The New Yorker, Jan

Kent State University, March 8, The QGP comes of age 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 Large Hadron Collider at CERN ALICE ATLAS CMS

Kent State University, March 8, The QGP comes of age Jet quenching at the LHC Pb+Pb at 5.5 TeV: First ion collisions 2008 qualitatively new probes  enormous reach in jet energy P. Jacobs and M. van Leeuwen Nucl. Phys A774, 237 (2006)

Kent State University, March 8, The QGP comes of age Jets and hadrons at RHIC II B.I. Abelev et al., PRL 97, (2006) RHIC II (x 10 luminosity upgrade): also has significant kinematic reach (jets to ~60-70 GeV)

Kent State University, March 8, The QGP comes of age What is interesting about high E T jets at RHIC II and LHC? Precision QCD: the evolution of nucleon structure with Q 2 (= resolution of the probe) High E T jets at LHC and RHIC may provide similarly precise probes of hot QCD matter

Kent State University, March 8, The QGP comes of age ALICE HMPID Muon Arm TRD PHOS PMD ITS TOF TPC Size: 16 x 26 meters Weight: 10,000 tons EMCal

Kent State University, March 8, The QGP comes of age

Kent State University, March 8, The QGP comes of age U.S. Contribution to ALICE: EMCal a large electromagnetic calorimeter Approved by LHCC 9/28/ /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 Enables jet measurements in ALICE

Kent State University, March 8, The QGP comes of age 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/ Jet quenching  fragmentation strongly modified at p T hadron ~1-5 GeV  =ln( E Jet / p hadron ) p T hadron ~2 GeV Jet quenching

Kent State University, March 8, The QGP comes of age 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 Q 2 (E T )?

Kent State University, March 8, The QGP comes of age Summary RHIC has failed: the initial expectation of an ideal gas plasma of non-interacting quarks and gluons has not been met. Instead, something much more interesting has been found: The QCD Matter generated in RHIC collisions is the most perfect fluid known. Its dynamical transport properties are calculable from fundamental theory, perhaps including string theory. They are therefore at least as interesting as its thermodynamics properties. Controlled, quantitative study of these properties is under way at RHIC II and the LHC.