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Do We Understand Interactions of Hard Probes With Dense Matter ?

Do We Understand Interactions of Hard Probes With Dense Matter ?. Joint EIC & Hot QCD Workshop on Future Prospects of QCD at High Energy BNL - 20 July 2006. Berndt Mueller (YITP Kyoto & Duke University). It’s all about “Matter”. What’s the Matter? Probing the Matter

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Do We Understand Interactions of Hard Probes With Dense Matter ?

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  1. Do We UnderstandInteractions of Hard Probes With Dense Matter ? Joint EIC & Hot QCD Workshop on Future Prospects of QCD at High Energy BNL - 20 July 2006 Berndt Mueller (YITP Kyoto & Duke University)

  2. It’s all about “Matter” • What’s the Matter? • Probing the Matter • Understanding the Matter

  3. General comments A young field: ~10 years of serious theory, 5 years of data! We are still in the conceptual phase. A rich field – for theorists and experimentalists alike: Full of well defined questions and challenges. An exciting field – new, unanticipated phenomena are discovered at a rapid pace in theory and experiment.

  4. Part I What’s the Matter?

  5. Chiral symmetry restored Critical end point ? QGP Entropy density RHIC Coexistence region Hadronic matter EIC Color SC Chiral symmetry broken Neutron stars Color charge density CGC Nuclei Baryon density CEBAF Saturation QCD phase diagram

  6. Past and future of QCD • The first 30 years of QCD were concerned (at the perturbative scale Q2) with single parton distributions: PDF’s, FF’s, GPD’s. • The future - exploration of multi-parton (N 2) correlations. These are generally: • Higher-twist effects (suppressed by powers of Q2). • Substantial effects in perturbative Q2 range require high parton densities: • A  1, x  0, dN/dy large.

  7. x2 x1 x1’ J/Y Parton correlations

  8. Part II Probing the matter

  9. central Ncoll = 975  94 Theoretical tools: Factorization QCD factorization: ppp0 AuAup0 Medium modifies the fragmentation function D(z) “Higher twist”

  10. High-energy parton loses energy by rescattering in dense, hot medium. q q “Jet quenching” = parton energy loss Described in QCD as medium effect on parton fragmentation: Medium modifies perturbative fragmentation before final hadronization in vacuo. Roughly equivalent to an effective shift in z: Important for controlled theoretical treatment in pQCD: Medium effect on fragmentation process must be in perturbative q2 domain.

  11. L q q g L q q Mechanisms High energy limit: energy loss by gluon radiation. Two limits: (a) Thin medium: virtuality q2 controlled by initial hard scattering (LQS, GLV) (b) Thick medium: virtuality q2 controlled by rescattering in medium (BDMPS) Trigger on leading hadron (e.g. in RAA) favors case (a). Low to medium jet energies: Collisional energy loss is competitive! Especially when the parent parton is a heavy quark (c or b).

  12. q L q q q g Scattering power of the QCD medium: Radiative energy loss Radiative energy loss: Scattering centers = color charges Density of scattering centers Range of color force

  13. Higher twist formalism

  14. x quark x - a b + x x = 0 Eikonal formalism Kovner Wiedemann Gluon radiation: Radiation probablility ~ correlation function C along forward light cone Nonperturbative definition of q-hat Gluonic energy density  correlation length

  15. (3+1)-D world horizon q-hat in AdS/CFT Liu, Rajagopal, Wiedemann, hep-ph/0605178

  16. Dynamic medium Thin medium: opacity expansion (GLV) works well for leading hadron assumes perturbative scattering and simplified evolution of the medium

  17. I. Vitev, hep-ph/0603010 Modeling sensitivity Surface emission of leading hadrons Details of modeling of the medium and probability distribution P(DE) of energy loss are very important. Average interaction length L is not appropriate. Value of q-hat is very sensitive to modeling details. Renk & Ruppert

  18. Data suggest large energy loss parameter: Eskola et al. RHIC Dainese, Loizides, Paic pT = 4.5–10 GeV Energy loss at RHIC Present calculations use simplified geometry and evolution models.

  19. A. Majumder – HT formalism with realistic evolution  RHIC data sQGP? ? QGP Pion gas Cold nuclear matter q-hat at RHIC Caveat: Details of medium evolution are important for quantitative extraction of q-hat from data!

  20. Along axis Off axis The QGP is a “windy” place Longitudinally and transversely flowing medium distorts jet cone T. Renk, J. Ruppert, PRC 72 (2005) 044901

  21. Vitev et al (GLV) Armesto et al (ASW) LHC Flat or rising RAA ? Extrapolations to LHC energy vary widely due to modeling differences:

  22. q_hat = 0 GeV2/fm dNg/dy = 1000 q_hat = 4 GeV2/fm q_hat = 14 GeV2/fm Charm energy loss From “non-photonic” electrons: Very surprising, b/c radiative energy loss of heavy quarks should be suppressed  Reconsider collisional energy loss mechanism (Mustafa & Thoma) S. Wicks et al nucl-th/0512076

  23. f Reaction plane correlations Quenching effect in non-central collisions depends on direction of jet relative to the collision plane: Allows for limited (!) test of L dependence!

  24. 8 < pT(trig) < 15 GeV/c Di-jet correlations Back-to-back leading hadrons are quadratically suppressed! Away-side jet trigger T. Renk J. Ruppert

  25. Photon tagged jets T. Renk, hep-ph/0607166 • “Golden” channel: q + g q + g. • Photon tags pT (and flavor - u/d quark!) of scattered parton. • Can be used to perform jet tomography (RAA does not work) • Important baseline and calibration for (opposite side) di-hadron tomography. RAA does not discriminate ? g-jet discriminates models

  26. g q g Hard Probes 2006, June 15, 2006 – G. David, BNL Medium-pT photons Turbide, Rapp, Gale PRC 69 014903 (2004) t0 = 0.33 fm/c, T = 370 MeV Jet induced contribution R.J. Fries, BM, D.K. Srivastava, PRL 90 (2003) 132301

  27. Part III Understanding the Matter

  28. Where does the “lost” energy go? p+p Au+Au Away-side jet Trigger jet Lost energy of away-side jet is redistributed to rather large angles!

  29. 2.5 < pT,trigger < 4.0 GeV 1.0 < pT,assoc < 2.5 GeV PHENIX STAR Preliminary Angular correlations Backward peak of correlated hadrons shifts sideways when pT window of associated hadrons is lowered! Deflection of primary backward parton – or extended shower of secondary particles associated with quenched backward parton?

  30. Cent=0-5% near near Medium Medium away away deflected jets mach cone Conical Flow vs Deflected Jets STAR Data J. Ulery, Hard Probes 2006

  31. Theorists’ concepts (Colorless or colorful) sonic shockwave: H. Stöcker, Nucl. Phys. A 750:121-147 (2005), J. Casalderrey-Solana & E. Shuryak, hep-ph/0411315, J. Ruppert & B.M., Phys. Lett. B 618:123-130 (2005), T. Renk & J. Ruppert, hep-ph/0509036 Trigger jet Localized heating of medium: A. Chaudhouri, U. Heinz, nucl-th/0503028 Trigger jet Large Angle Gluon Emission: Ivan Vitev, Phys.Lett.B630:78-84,2005 Cherenkov (-like) radiation: A. Majumder & X. N. Wang, nucl-th/0507062, V. Koch et. al., nuclt-th/0507063, I. Dremin, hep-ph/0507167 Trigger jet

  32. Longitudinal (sound) modes Transverse modes “Colored” sound ? Normal sound Signal: Mach cones Signal: Cherenkov rings Collective QGP modes

  33. Sound wave Heating Away side jet Trigger jet Mach cone phenomenology Fraction f of isentropic energy deposition into sound mode Fraction (1-f) of dissipative energy deposition into heat – requires viscous, turbulent flow behind leading parton. Casalderrey et al., hep-ph/0602183 Spectrum of sonic matter Thermal spectrum

  34. Fries, Bass, BM PRL 94, 122301 (2005) hD = h1-h2 Two-point velocity correlations among 1-2 GeV/c hadrons away-side same-side fD = f1-f2 Dihadron correlations An explanation for compatibility dihadron correclations with recombination? • Parton correlations naturally translate into hadron correlations. • Parton correlations likely to exist in the quasithermal regime, created as the result of jet-medium interactions.

  35. Dijet rapidity correlation Trigger vertex distribution Mach cone phenomenology II Renk - Ruppert, hep-ph/0605330 Renk, nucl-th/0607035 Rapidity cut effects Flow effects on correlation

  36. Wakes in the QGP J. Ruppert and B. Müller, PLB 618 (2005) 123 Angular distribution depends on energy fraction in collective mode and propagation velocity Mach cone requires collective mode with w(k) < k. Question: Is there a colored mode in this kinematic regime? Or – can color field couple “superefficiently” to sound mode?

  37. Mach cone in AdS/CFT Mach angle J.J. Friess et al. hep-th/0607022 N = 4 SYM

  38. The AdS5/CFT wake Subsonic Angular distributions for v = 0.95 and different k. Supersonic

  39. Summary • Jets are rich anddiscriminative probes of the medium: • Strong energy loss agrees semi-quantitatively with theory; • Probes of a well defined transport coefficient: q-hat; • Quantitative determination of q-hat requires sophisticated and realistic description of medium evolution (transport); • Rigorous, nonperturbative calculation of q-hat in QCD ? • Relative weight of radiative and collisional energy loss ? • Dependence on primary parton flavor ? • Interaction of radiated energy with medium probes dissipation mechanisms and collective QGP modes. • Jet studies at the LHC will complement and greatly extend the RHIC measurements, but a lot remains to be explored at RHIC (heavy quarks, photon-jet correl’s, di- and multi-hadron correl’s with particle ID, etc.)

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