Heavy Ion Collisions at the LHC startup: p+p 2007 Pb+Pb 2007/8 Urs Achim Wiedemann Physics Department, CERN 9 October 2004 ALICE-Korea Workshop

Kinematics at the LHC small-x: determines properties of the medium large Q : determines probes of the medium 2

Hadronization versus Thermalization of Partons h h h in vacuum in QGP 1Ge V 10 GeV 100 GeV 100 fm 1 fm Dynamics of hadronization Jet absorption Jet heating Dynamics of the bulk Partonic equilibration processes

Setting the Transverse Momentum Scales ● High parton thermalization jet tomography ● Intermediate dynamics of hadronization ● Soft bulk dynamics

High pt Partons as Probes of Dense Matter 1. hadronic high-pt spectra

Centrality Dependence: Au+Au vs. d+Au Preliminary DataFinal Data ● Final state suppression ● Initial state enhancement

The medium-modified Final State Parton Shower Medium characterized by transport coefficient: Baier, Dokshitzer, Mueller, Peigne, Schiff (1996); Zakharov (1997); Wiedemann (2000); Gyulassy, Levai, Vitev (2000); Wang... Salgado,Wiedemann PRD68: (2003) ● energy loss of leading parton ● pt-broadening of shower

Quenching of Leading Hadroproduction suppression of leading hadrons governed by X.N. Wang, nucl-th/ Centrality dependence tests interplay of density and geometry E.Wang, X.N. Wang, PRL 89 (2002) ; Gyulassy, Vitev, Wang PRL 89 (2002) ; Salgado, Wiedemann PRL 89 (2002) suppression implies scaling X.N. Wang, nucl-th/

Eskola, Honkanen, Salgado, Wiedemann, 2004 Fragility of leading hadron spectra as hard probe ● surface emission limits sensitivity to density

Testing the Mechanism: E-Loss of Heavy Quarks ● medium-induced radiation fills the dead-cone massive massless dead cone Armesto, Salgado, Wiedemann, hep-ph/ ● vacuum radiation suppressed in the dead-cone Dokshitzer, Kharzeev, PLB 519 (2001) 199 ● total energy loss comparable but smaller than in the massless case Armesto, Salgado, Wiedemann, hep-ph/ Uncertainties: - massive quarks are slower - finite energy corrections large (hadronization inside medium relevant for higher pt) Djordjevic, Gyulassy, nucl-th/ B.W. Zhang, E. Wang, X.N. Wang, nucl-th/

Beyond Leading Hadroproduction Where does this associated radiation go to ? How does this parton thermalize ?

Jets in Heavy Ion Collisions at the LHC ● Experiments at LHC will detect jets above background ● How can we quantify their medium modifications above background ? What do we learn from them ? A. Accardi et al., hep-ph/ CERN TH Yellow Report

'Jet Heating': Jet Shapes and Jet Multiplicities Salgado, Wiedemann, hep-ph/ , Phys. Rev. Lett. in press ● Energy fraction in fixed jet cone weakly dependent on medium medium vacuum ● Multiplicity within small jet cone broadens significantly unaffected by high-multiplicity background !. kt

Armesto, Salgado, Wiedemann, 2004 Asymmetric Jet Shapes test Collective Flow ● Hard partons are not produced in the rest frame comoving with the medium test this

Theory predicts ● Characteristic L- dependence ● Dependence on the identity of the parent parton ● Relation between energy loss and pt-broadening ● Dependence on collective motion and energy density of medium Experimental Tests ➔ leading hadron spectra as function of centrality and orientation w.r.t. reaction plane ➔ jets and jet-like correlations ➔ charmed (beauty) hadrons ➔ - ratio at high pt ➔ hadroproduction associated to high-pt trigger particles ➔ jet shapes and jet multiplicity distributions

Intermediate pt Fragmentation inside the medium: what happens now ?

Breakdown of Independent (pert.) Fragmentation ● Jet quenching does not affect ratio in contrast to observation ● How does the bleaching of color charges proceed dynamically ? a bare colored parton dressed quark or color string or diquark or... 'bleached' hadron Recombination String Fragmentation Diquark Dressing S. Bass pQCD:

Fragmentation versus Recombination start from quark spectrum: ● Fragmentation: ● Recombination recombination fragmentation Exp. spectrum: recombination dominates Powerlaw tail: fragmentation dominates Range of applicability: intermediate pt upper bound on pt ● Quark number scaling of v2 Voloshin, QM2002, nucl-ex/

Soft pt Statistics and Dynamics of the Bulk

Hadronization in the Grand Canonical Ensemble Which microscopic dynamics turns quarks and gluons into hadrons ? ● Recent refinements: - system size dependence - hadronization of charm ● Hadronization of a QGP in chemical equilibrium at (T, ) ? de Forcrand, Philipsen 1, Fodor, Katz Allton et al. D'Elia, Lombardo ● Hadron yields and ratios fitted by statistical model in terms of (T, )

'Blastwave Model': Snapshot at Freeze-out ● Recent refinements: anisotropy What is the microscopic dynamics determining these distributions ? Lisa, Retiere, nucl-th/ ● Low pt Hadron Spectra fitted by - local thermal equilibrium - collective flow space-time geometry: HBT ?, asHBT !

Hydro: Learning from Agreements or Deviations ? Hirano, Nara, nucl-th/ Kolb, Rapp PRC67 (2003) Molnar, Gyulassy, NPA 697 (2002) 495 ● How to understand the range of validity of hydrodynamics ? Opacity Problem ! - hadronization may change flow by by a large factor (2-3) - realistic freeze-out condition (beyond Cooper-Frye) needed for some data, e.g. HBT ● Hydrodynamics + statistical hadronization works up to for - pt -spectra - rapidity distribution - elliptic flow Molnar, Voloshin PRL 91 (2003) Hadronization matters ! Sinyukov, Akkelin, Hama, PRL 89 (2002) Akkelin, Braun-Munzinger, Sinyukov, NPA710 (2002) 439 Tomasik, Wiedemann PRC68 (2003)

Saturation Physics and its possible tests heavy ion collisions non-linear small-x evolution perturbatively calculable High density: but Balitsky; Kovchegov; Jalilian-Marian,Kovner, Leonidov, Weigert;...

The projectile: nuclear parton distribution at small x ● lepton-nucleus scattering at small x ● unintegrated target gluon distribution at initial rapidity ● Evolution with rapidity: Balitsky 1994, Kovchegov 1999 [ ] *

Geometric Scaling at small x ● Solution of BK-equation depends on saturation scale only ● Data on lepton-proton scattering show geometric scaling Stasto, Golec-Biernat, Kwiecinski, 1999 ● Data on lepton-nucleus scattering Armesto, Salgado, Wiedemann, 2004

The Day 1 Observable at RHIC and LHC signal proportional to multiplicity PHOBOS, Phys. Rev. Lett. 85 (2000) 3100 Au+Au at RHIC ● Multiplicity important as centrality measure and for estimates of energy density Bjorken, 1982

A model for the multiplicity in A+A Ansatz: Armesto, Salgado, Wiedemann, 2004 provides fair description of multiplicity and its centrality dependence at SPS and RHIC

Multiplicity: expectations from naïve extrapolations Armesto, Salgado, Wiedemann hep-ph/ our model logarithmic extrapolation figures from G. Roland

● What determines the initial energy density created in nucleus-nucleus collisions ? ● What is the nature of equilibration processes and what is their time scale ? ● What is the dynamics of hadronization and how does it depend on system size ? ●... The RHIC-ness of accessible Scales and Questions 1Ge V 10 GeV 100 GeV 100 fm 1 fm dynamics of hadronization Jet absorption Onset of thermalization “DIS on QGP” dynamics of the bulk + A-dependence + - dependence + d-Au collisions + LHC