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Jet Quenching at RHIC and the LHC

Jet Quenching at RHIC and the LHC. William Horowitz Columbia University November 1, 2006. With many thanks to Simon Wicks, Azfar Adil, Magdalena Djordjevic, and Miklos Gyulassy. Outline. What a difference the LHC makes! HUGE disagreement over LHC predictions Why there’s a difference

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Jet Quenching at RHIC and the LHC

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  1. Jet Quenching at RHIC and the LHC William Horowitz Columbia University November 1, 2006 With many thanks to Simon Wicks, Azfar Adil, Magdalena Djordjevic, and Miklos Gyulassy.

  2. Outline • What a difference the LHC makes! • HUGE disagreement over LHC predictions • Why there’s a difference • Why we’re right (hopefully robustly) • P0, P0, P0…

  3. LHC Predictions WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

  4. BDMPS-Based Predictions K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005) A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)

  5. Suppression of BDMPS • LHC predictions require an extrapolation from RHIC • Their pQCD-based controlling parameter qhat must be nonperturbatively large to fit RHIC data -pQCD gives qhat = c e3/4, where c ~ 2; they require c ~ 8-20 for RHIC -Needed because radiative only energy loss (and Pg0 > 1?); R = (1/2) qhat L3 K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)

  6. BDMPS Extrapolation to the LHC • Importance of medium density • qhat ~ rscatterers • EKRT used => rLHC ~ 7 rRHIC • qhat goes from 14 at RHIC to 100 at the LHC! • Almost all the energy loss is in d(e-1) part of P(e)

  7. Asymptopia at the LHC Asymptotic pocket formulae: DErad/E ~a3 Log(E/m2L)/E DEel/E ~a2 Log((E T)1/2/mg)/E WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

  8. LHC Production Spectra • Much flatter power law and asymptotic jet energies allows for easy interpretation of LHC predictions

  9. LHC Conclusions • LHC appears to reach jet asymptopia where pocket formulae hold • Lack of fragility means pions will make a good, independent probe of the density • With current predictions, the momentum dependence of RAA at LHC should distinguish between BDMPS and GLV type loss models

  10. A Quick Update on Fragility

  11. Jets as a Tomographic Probe • Requires: • Theoretical understanding of underlying physics (esp. quenching mechanisms) • Mapping from the controlling parameter of the theory to the medium density • Sensitivity in the model + data for the measurement used (FRAGILITY???)

  12. Recall the BDMPS-based Plots The lack of sensitivity needs to be more closely examined because (a) unrealistic geometry (hard cylinders) and no expansion and (b) no expansion shown against older data (whose error bars have subsequently shrunk (a) (b) K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005) A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)

  13. Our Jets Probe the Volume and are Sensitive to the Medium S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076 WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

  14. BDMPS with Realistic Geometryis Not Fragile! T. Renk and K. J. Eskola, hep-ph/0610059

  15. Heavy Quark Puzzle

  16. Before the e- RAA, the picture looked pretty good: • Null Control: RAA(g)~1 Y. Akiba for the PHENIX collaboration, hep-ex/0510008 • Consistency: RAA(h)~RAA(p) • GLV Prediction: Theory~Data for reasonable fixed L~5 fm and dNg/dy~dNp/dy

  17. Theory v2 too small Fragile Probe? But with Hints of Trouble: A. Drees, H. Feng, and J. Jia, Phys. Rev. C71:034909 (2005) (first by E. Shuryak, Phys. Rev. C66:027902 (2002)) K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)

  18. What Can Heavies Teach Us? • Provide a unique test of our understanding of energy loss • Mass => Dead Cone => Reduction in E loss = Bottom Quark • (Gratuitous Pop Culture Reference)

  19. Entropy-constrained radiative-dominated loss FALSIFIED by e- RAA Problem: Qualitatively, p0 RAA~ e- RAA

  20. Inherent Uncertainties in Production Spectra How large is bottom’s role? M. Djordjevic, M. Gyulassy, R. Vogt, S. Wicks, Phys. Lett. B632:81-86 (2006) • Vertex detectors could de-convolute the e- contributions N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257

  21. The BDMPS-Z-WS Approach • Increase to 14 to push curve down • Fragility in the model allows for consistency with pions N. Armesto, M. Cacciari, A. Dainese, C. A. Salgado, U. A. Wiedemann, hep-ph-0511257

  22. What Does Mean? We believe it’s nonperturbative: • a = .5 => dNg/dy ~ 13,000 “Proportionality constant ~ 4-5 times larger than perturbative estimate” K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005) “Large numerical value of not yet understood” R. Baier, Nucl. Phys. A715:209-218 (2003) U. A. Wiedemann, SQM 2006

  23. Is this Plausible?Renk says No T. Renk and K. J. Eskola, hep-ph/0610059

  24. Our Results • Inclusion of elastic decreases the discrepancy • Direct c and b measurements required to truly rule out approaches S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

  25. LHC Predictions for Heavies WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

  26. Conclusions III • Elastic loss cannot be neglected when considering pQCD jet quenching • Coherence and correlation effects between elastic and inelastic processes that occur in a finite time over multiple collisions must be sorted out • Fixed a must be allowed to run; the size of the irreducible error due to integration over low, nonperturbative momenta, where a > .5, needs to be determined • Large uncertainties in ratio of charm to bottom contribution to non-photonic electrons • Direct measurement of D spectra would help separate the different charm and bottom jet dynamics

  27. Backup Slides

  28. Our Extended Theory • Convolve Elastic with Inelastic energy loss fluctuations • Include path length fluctuations in diffuse nuclear geometry with 1+1D Bjorken expansion

  29. Significance of Nuclear Profile • Simpler densities create a surface bias Hard Cylinder Hard Sphere Woods-Saxon Illustrative Only! Toy model for purely geometric radiative loss from Drees, Feng, Jia, Phys. Rev. C.71:034909

  30. Null Control: RAA(g)~1 Y. Akiba for the PHENIX collaboration, hep-ex/0510008 • Consistency: RAA(h)~RAA(p)

  31. Elastic Can’t be Neglected! M. Mustafa, Phys. Rev. C72:014905 (2005) S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

  32. Length Definitions • Define a mapping from the line integral through the realistic medium to the theoretical block • where • Then

  33. Geometry Can’t be Neglected! • P(L) is a wide distribution • Flavor independent • Flavor dependent fixed length approximations LQ’s not a priori obvious S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076

  34. Comparison to Vitev

  35. Increasing dNg/dy

  36. Our Extended Theory • Convolve Elastic with Inelastic energy loss fluctuations • Include path length fluctuations in diffuse nuclear geometry with 1+1D Bjorken expansion • Separate calculations with BT and TG collisional formulae provide a measure of the elastic theoretical uncertainty

  37. Qhat = c eps^3/4 \propto rho (density of scattering centers) • pQCD=> c~=2 • To fit RHIC, c ~ 8-20 • Extend to LHC, everything crushed to nothing

  38. BDMPS RHIC p’s Huge qhat needed! (a) (b) K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005) A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005) Note: fragility due to lack of Bjorken expansion

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