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Jets in Heavy Ion Collisions at RHIC and at the LHC

Jets in Heavy Ion Collisions at RHIC and at the LHC. Urs Achim Wiedemann CERN Physics Department TH Division. Hamburg, 28 September 2005. in QGP. h. in vacuum. h. h. Partonic equilibration processes. Dynamics of the bulk. Dynamics of hadronization. 100 fm. Jet absorption.

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Jets in Heavy Ion Collisions at RHIC and at the LHC

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  1. Jets in Heavy Ion Collisionsat RHIC and at the LHC Urs Achim Wiedemann CERN Physics Department TH Division Hamburg, 28 September 2005

  2. in QGP h in vacuum h h Partonic equilibration processes Dynamics of the bulk Dynamics of hadronization 100 fm Jet absorption Jet modification 1 fm 10 GeV 1GeV 100 GeV Times scales: hadronization vs.thermalization

  3. Medium characterized by transport coefficient: • How much energy is lost ? Characteristic gluon energy Phase accumulated in medium: , where Number of coherent scatterings: Gluon energy distribution: Average energy loss Parton energy loss - a simple estimate

  4. Baier, Dokshitzer, Mueller, Peigne, Schiff (1996); Zakharov (1997); Wiedemann (2000); Gyulassy, Levai, Vitev (2000); Wang ... Medium characterized by transport coefficient: • pt-broadening of shower • energy loss of leading parton Salgado,Wiedemann PRD68:014008 (2003) The medium-modified Final State Parton Shower

  5. = 1.5, 1.0, 0.5, 0 Energy Loss in a Strongly Expanding Medium • In A-A collisions, the density of scattering centers is time-dependent: Salgado, Wiedemann PRL 89, 092303 (2002) • Dynamical Scaling Law: same spectrum obtained for equivalent static transport coefficient: • Calculations for a static medium apply to expanding systems Rescaled spectrum

  6. Azimuthal particle distribution at RHIC in qualitative agreement with hydrodynamic picture of the collision PRC 72 (05) 014904 200 GeV Au+Au min-bias bounce squeeze Elliptic flow: hallmark of a collective phenomenon

  7. D. Teaney Molnar, Gyulassy, NPA 697 (2002) 495 Molnar, Gyulassy, NPA 697 (2002) 495 2 2 1 1 3 3 4 4 5 5 Elliptic Flow vs. Theory: open questions • Viscosity Problem/Property Hydro simulations require an extremely small ratio of viscosity over entropy. • Can one calculate viscosity in QCD ? • Are there independent tests that • dissipative processes are negligible ? • Opacity Problem Parton cascades require unnatural large partonic cross sections How can we test the microscopic dynamics underlying collectivity?

  8. High pT Hadron Spectra Glauber model

  9. partonic energy loss Jet Quenching: Au+Au vs. d+Au • Initial state enhancement • Final state suppression

  10. Eskola, Honkanen, Salgado, Wiedemann Nucl Phys A747 (2005) 511 • Why is RAA ~ pT-independent? • Trigger bias more severe for large pT • Why is RAA = 0.2 natural ? • Surface emission limits sensitivity to ? • Matter is so opaque, even 20 GeV pions are stopped! The fragility of leading hadrons

  11. Near-side RAA Trigger Dainese, Loizides, Paic, hep-ph/0406201 Adams et al. PRL 91 (2003) Adler et al. PRL 90:082302 (2003) Away-side IAA Centrality dependence, back-to-back correlations

  12. Time-averaged is very large. Dynamical scaling implies • traces energy density RHIC data sQGP QGP for the values favored by RHIC-data “Opacity problem” Pion gas Cold nuclear matter The produced matter is opaque - why ? R. Baier, NPA 715 (2003) 209

  13. How does this parton thermalize ? Where does this associated radiation go to ? How can one determine the dependence on parton identity ? Testing the microscopic dynamics expected to underlie jet quenching

  14. (1) q_hat = 0 GeV2/fm (4) dNg / dy = 1000 (2) q_hat = 4 GeV2/fm (3) q_hat = 14 GeV2/fm Inclusive single electron spectrum in Au+Au • Parton energy loss is sensitive • to parton identity • Single electron spectrum at high • transv. Momentum dominated by • b- and c-decays. • Observed suppression consistent • with quenching of light hadrons. • (But significant uncertainties in ratio • of b/c perturbative cross section and • in b/c fragmentation.)

  15. Armesto, Dainese, Salgado, Wiedemann, PRD71:054027,2005 Massless “c/b” Massive c/b At high : • Charm is sufficiently light, • so that double ratio tests: • Beauty is sufficiently heavy, • so double ratio dominated • by mass dependence: Future tests at RHIC and at the LHC

  16. Longitudinal Jet Heating Borghini,Wiedemann, hep-ph/0506218 • Medium expected to soften • and increase the longitudinal • multiplicity of ‘true jets’. • Softening in qualitative agreement • with triggered particle correlations. • Awaits detailed test at the LHC.

  17. Jets in pionic winds and partonic storms If medium shows strong collective flow, what are additional measurable consequences at LHC ? Armesto, Salgado, Wiedemann, Phys. Rev. Lett. 93 (2004) 242301 Hard partons are not producedin the rest frame comoving withthe medium Flow effect

  18. Ruppert, Renk, hep-ph/0507075 Au+Au Flow effects on Hard Probes • Very strong transverse flow may • resolve the opacity problem with flow without flow • Strong longitudinal flow may account for broadened • multiplicity distribution associated to high-pt trigger particles. Data: D. Magestro (STAR), preliminary

  19. Partonic equilibration processes Dynamics of the bulk Dynamics of hadronization 100 fm Jet absorption Jet modification 1 fm 10 GeV 1GeV 100 GeV Hard high-Q2 processes are abundant at collider energy

  20. BACK-UP

  21. High pT: parton thermalization jet tomography • Intermediate pT: dynamics of hadronization • Soft pT: bulk dynamics Setting the transverse momentum scales

  22. Jets in Heavy Ion Collisions at the LHC A. Accardi et al., hep-ph/0310274 CERN TH Yellow Report • Experiments will detect jets above background • How can we characterize the medium-modification of these jets • above background ?

  23. Parton energy loss as a test of viscosity ? • In an ideal liquid, energy does • not dissipate but is radiated as • sound wave Mach cone

  24. Solve Dirac equation for partonic projectile in external color field of the medium Parton Propagation in Dense Matter Leading order O(E0) scattering determined by eikonal Wilson line During scattering, transverse coordinates are frozen, color rotates 2. Leading energy correction transverse Brownian motion “Furry approximation”

  25. Wiedemann, NPB 588 (2000) 303 Radiation off produced parton Target average includes Brownian motion: Two approximation schemes: Harmonic oscillator approximation: Opacity expansion in powers of BDMPS transport coefficient The medium-modified Final State Parton Shower

  26. Expand path intergral: Zeroth order: 2 First order: Parton cascade limit: L 2 2 Rescattering of vacuum term + + + + Bertsch-Gunion 2 Opacity Expansion

  27. Triggering on high-pt hadrons, one selects a biased parton fragmentation pattern: Trigger Bias in high-pt hadron production • A bias favoring hard fragmentation, determined by steepness of spectrum: • A bias favoring small in-medium path length (surface emission) • A bias favoring initial-state pt-broadening in the direction of the trigger

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