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Dihadron Tomography of High Energy AA Collisions in NLO pQCD

Dihadron Tomography of High Energy AA Collisions in NLO pQCD. Hanzhong Zhang Department of Physics, Shandong University Institute of Particle Physics, Central China Normal University. 1) Phys. Rev. Lett. 98(2007)212301 2) J. Phys. G. 34(2007)S801 3) To be submitted.

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Dihadron Tomography of High Energy AA Collisions in NLO pQCD

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  1. Dihadron Tomography of High Energy AA Collisions in NLO pQCD Hanzhong Zhang Department of Physics, Shandong University Institute of Particle Physics, Central China Normal University 1) Phys. Rev. Lett. 98(2007)212301 2) J. Phys. G. 34(2007)S801 3) To be submitted. Collaborators: Enke Wang Joseph F. Owens Xin-Nian Wang Jinan, Jan. 9, 2008

  2. Outline • Introduction • Modified fragmentation function model • Numerical analysis on single hadron and dihadron production • Conclusions

  3. I. Introduction 1. What is “Dihadron tomography” ? 1) Medical x-ray tomography: see inside a “bone” by x-ray. 2) Jet tomography: see inside “QGP” by a parton jet, not only by single jet, but also by dijet. 3) Hadron/Dihadron tomography: we can’t “catch” a parton jet/dijet, but can “catch” a hadron/dihadron.

  4. leading particle hadrons q q hadrons leading particle Leading particle suppressed hadrons q q hadrons N-N collision A-A collision leading particle suppressed 2. How to know a tomography of QGP ? ---- Jet Quenching ! Jet quenching: Induced by multiple scattering in QGP medium, a parton jet will radiate gluon and lose its energy.

  5. 3. Why NLO study? LO analysis of jet quenching in AA : A factor K=1.5-2 was put by hand to account for higher order corrections pQCD Parton Model 2→2 processes (tree level) Jet quenching in 2→2 processes

  6. NLO (Next to Leading Order ) corrections: K is absent One-loop corrections Jet quenching in 2→3 processes 2→3processes (tree level) Jeff. Owens , PRD65(2002)034011; B.W. Harris and J. Owens, PRD65(2002)094032. NLO:More stronger quenching;More clearer QGP picture.

  7. 4. Why dihadron tomography study? • Single hadron suppression factor is found to be fragile to probe the dense matter. • K. J. Eskola , et al, NPA747 (2005) 511-529 • One of the motives of this work: • How about dihadron? fragile or robust?

  8. II. Modified fragmentation functions model Jet Quenchingeffect in AA is incorporated via a model of modified fragmentation functions: (X. -N. Wang , PRC70(2004)031901) where Jet energy loss Two contributions from jets in vacuum and medium!

  9. the averaged scattering number, It determines the thickness of the outer corona where a parton jet survives in the overlapped region. the gluon density distribution,

  10. In 1-demension expanding medium, the total energy loss is written as a path integration: The energy loss per unit lenth with detailed balance: (Enke Wang and Xin-Nian Wang, PRL87(2001)142301) An energy loss parameter proportional to the initial gluon density

  11. is equivalent to where is a jet transport or energy loss parameter, In BDMPS calculation for the radiative parton energy loss, Baier, Dokshitzer, Mueller, Peigne, Schiff, NPB484(1997)265 reflects the ability of the medium to “quench” jets. By Wang2 and BDMPS formulas, estimate the average jet transport parameter by J. C. Solana and X. -N. Wang, hep-ph/0705.1352

  12. III. Numerical analysis on single hadron and dihadron production 1. Single hadron tomography 2. Dihadron tomography 3. Estimate jet transport parameter 4. Comparison between different shadowing 5. LHC predictions

  13. 1. Single hadron tomography single inclusive or production

  14. Set ,since p_T spectra in pp is not at all sensitive to the choice of The invariant p_T spectra of single hadron With ,p_T spectra in AA is not also sensitive to the choice of

  15. is not sensitive to the initial gluon density Nuclear modification factor is 10% larger than

  16. is not sensitive to ,and Centrality dependence

  17. loses its effectiveness as a good probe of dense matter 1.68 isa fragile probe of dense matter. Similar to the study by K. J. Eskola , H. Honkanen, C. A. Salgado, U. A. Wiedemann, NPA747 (2005) 511-529 The bigger is, the flatter is. Why the single hadron tomography is fragile to probe the dense matter?

  18. Single hadron is dominated by vertical surface emission y emission surface Single hadron x parton jet coronathickness completely suppressed Color strength =single hadronyield from partons in the square

  19. 2. Dihadron tomography Is there a robust probe of the dense matter produced in AA collisions? Let’s see dihadron production! Trigger one hadron of a dihadron, check the other hadron --- the associated hadron

  20. The dihadron spectra in Au+Au collisions No jet quenching in d+Au, Fit dAu data by pp result to fix scales, Invariant mass

  21. The dihadron suppression factor in Au+Au collisions

  22. If no jet quen-ching,

  23. Comparison between single hadron and dihadron tomography in Au+Au collisions dihadron single hadron

  24. 1.68 The curve is steeper thanwhen Dihadron is a robust probe of dense matter.

  25. comparison between single hadron and dihadron suppression factor for for dihadron for single

  26. Single hadron is dominated by verticalsurface emission Why does the dihadron behave more robust than single hadron to probe the dense matter? dihadron ?

  27. Dihadron is from tangential surface emission + punch-through jets N y triggered hadron x associated hadron partonic di-jet tangential S punch-through jets 25% left Color strength =dihadronyield from partons in the square

  28. 3. Estimate jet transport parameter

  29. 4. Comparison between different shadowing p+Au@RHIC 200GeV

  30. Au+Au@RHIC 200GeV single hadron dihadron Single hadron and dihadron are all not sensitive to different shadowing at RHIC

  31. LHC 5. LHC predictions is estimated as 4.5-5. 5 GeV/fm at LHC Trigger:20GeVat LHC Dihadron robust Single hadron fragile

  32. increases while decreases with collision energy. RHIC LHC There are much more punch-through jets in higher energy AA collisions,

  33. Different shadowing in p+Pb@LHC 5500GeV

  34. Different shadowing in Pb+Pb@LHC 5500GeV dihadron single hadron Dihadron sensitive to different shadowing because of much more punch-through jets. Single hadron not sensitive to different shadowing.

  35. 2) Punch-through jets contributing to hadron spectra at LHC

  36. Why is only Dihadron Iaa at LHCsensitive to different shadowing parameterizations, HIJ, EKS, nDS, nPDF? H. Zhang, J.F. Owens, E. Wang and X.-N. Wang , hep-ph/0000008 1) Punch-through jets are created from centralsystem region;2) Initial partons participating in stronginteraction in centralregionshould be associated with stronger shadowing effectsthan those initial partons in the outer layer of the system;3) So punch-through jets manifest a strongshadowing effect. There are much more punch-through jet contributing to dihadron spectra at LHC than at RHIC. So does dihadron than single hadron.

  37. IV. Conclusions 1) Because of the stronger quenching effects, the single hadron is dominated by vertical surface emission; the dihadron is from tangential surface emission + punch-through jets. 2) The dihadron is more sensitive to the initial gluon density than the single hadron . When becomes insensitive in higher energy A+A collision, is a sensitive probe of dense matter. 3) -fit to both single and dihadron spectra can be achieved with a narrow range of the energy loss parameter at RHIC energy, it provide convincing evidence for the jet quenching description. 4) Dihadron Iaa at LHC is found to be able to distinguish different shadowing parameterizations.

  38. Thank for your attention! 谢谢！

  39. Hard sphere model

  40. the formula of spectra inAA nuclear modification factor

  41. (Shi-Yuan Li and Xin-Nian Wang , PLB527(2002)85) (Enke Wang and Xin-Nian Wang, PRL87(2001)142301) (B. B. Back et al. [PHOBOS collaboration], PRC70(2004)021902)

  42. Nuclear shadowing effects only in small pT region So in large pT, medium effects only come from Jet Quenching !!!

  43. The invariant p_T spectra of single hadron p-p data at 200GeV are used to fix scales,

  44. Invariant mass: How to fix scales: If no medium effects, (X. –N. Wang , PLB 595(2004)165

  45. The dihadron azimuthal distributions

  46. PRL95(2005)152301 The ratio between the yield/trigger in AA and in pp: If no jet quen-ching, 0.3

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