Punch-through Jets in A+A Collisions at RHIC/LHC

1. Punch-through Jets in A+A Collisions at RHIC/LHC Han-Zhong Zhang Institute of Particle Physics, Huazhong Normal University, China Collaborators: J. Owens, E. Wang and X.-N. Wang QuarkMatter2008 Feb. 4-10 , 2008

2. Outline • Introduction • Fragility of single/dihadron suppression factors • Single/dihadron spectra at RHIC/LHC • IV. Azimuthal angle anisotropy of single/dihadron spectra at RHIC/LHC • V. Conclusions

3. I. Introduction leading particle hadrons q q hadrons leading particle Leading particle suppressed hadrons q q hadrons N-N collision A-A collision leading particle suppressed What happens for a jet propagating inside QGP? Jet quenching: The hard jet loses a significant amount of its energy via radiating gluon induced by multiple scattering.

4. A NLO pQCD parton model with jet quenching in A+A Parton distribution functions NLO cross sections Nuclear geometry Jet Quenchingeffect in AA is incorporated via modified fragmentation functions. (X. -N. Wang , PRC70(2004)031901) Jet energy loss

5. Energy loss parameter Initial gluon density coefficient Parton jet energy loss per unit length: E. Wang , X. -N. Wang , PRL87(2001)142301) (a parameterization form of theory calculations) B. B. Back for PHOBOS, nucl-ex/0604017v1

7. II. Fragility of single/dihadron suppression factors Simultaneous fit of single/dihadron spectra single hadron dihadron In most central Au+Au

8. -fit to both suppression factors in most central Au+Au for dihadron Sharp concave Flat concave for single H. Zhang, J.F. Owens, E. Wang and X.-N. Wang , PRL 98(2007)212301 Iaa robust when Raa fragile at RHIC

9. Color strength: yield per unit area Surviving dijets:close and tangential tothe surface + punch-through dijets Surviving jets:close and perpendicular tothe surface single hadron dihadron Thickness of the outer corona

10. -fit to all single hadron Raa factors in Au+Au with different centrality bins at RHIC energy Normalized in most central Au+Au at 200GeV HIJING shadowing + JQ EKS98 shadowing + JQ Energy loss parameter

11. III. Single/dihadron spectra at RHIC/LHC At LHC Surface emission bias single hadron dihadron punch-jets

12. Comparisons for shadowing in single hadron spectra in p+A 4 kinds of shadowing parameterizations, (1)HIJ (S.-Y. Li and X.-N. Wang, PLB527(2002)85-91)(2)EKS(K.J. Eskola, V.J. Kolhinen and C.A. Salgado, Eur. Phys.J., C9 (1999) 61)(3)nPDF (M. Hirai, S. Kumano, and T.-H. Nagai, PRC70, (2004) 044905) (4)nDS(D. de Florian, R. Sassot, PRD69(2004) 074028) Shadowing depends on impact parameter in pA collisions. At RHIC At LHC No Quenching! Only shadowing!

13. Single/dihadron spectra with different shadowing in A+A at RHIC At RHIC single hadron dihadron Single/dihadron Raa/Iaa are all insensitive to different shadowing at RHIC

14. Single/dihadron spectra with different shadowing in A+A at LHC At LHC single hadron dihadron Single hadron Raa insensitive to different shadowing. Dihadron Iaa sensitive to different shadowing.

15. 1) Initial partons participating in stronginteraction in centralregionshould be associated with stronger shadowing effectsthan those initial partons in the outer layer of the system.2) Because of surface emission bias, single hadron Raa is insensitive to shadowing at RHIC/LHC.3) Punch-through jets are created from centralsystem region, and where the shadowing is stronger. 4) Punch-through jets at RHIC are greatly suppressed, so dihadron Iaa is also insensitive to shadowing at RHIC.5) Punch-through jets at LHC are released to dominate dihadron, so dihadron Iaa is sensitive to shadowing at LHC.

16. IV. Azimuthal angle anisotropy of single/dihadron spectra at RHIC/LHC v2 definitions in single/dihadron spectra For single hadron, For dihadron, Trig Asso Azimuthal anisotropy is probed by “single jets”. Azimuthal anisotropy is probed by “dijets”.

17. jets Azimuthal angle anisotropy manifested by jet quenching in high p_T single spectra single hadron at RHIC

18. Dihadron v2 > single hadron v2 dihadron v2 single hadron v2 For single hadron, the anisotropy is probed by quenched single jets which have a bias of surface emission.For dihadron, the anisotropy is probed by quenched dijets which have a bias of tangential surface emission.

19. v2@LHC > v2@RHIC single hadron v2 dihadron v2 LHC RHIC LHC RHIC Initial gluon density at LHC > RHIC

20. V. Conclusions 1) -fit to both single and dihadron suppression factors provides a convincing evidence for the jet quenching description. I_AA is robust to probe the dense matter when R_AA is fragile. 2) Punch-through jets are found to dominate high p_T dihadron production in Pb+Pb at LHC. Dihadron Iaa at LHC is able to distinguish different shadowing parameterizations. 3) Dihadron v2 > single hadron v2 at RHIC/LHC, and v2@LHC > v2@RHIC for both single/dihadron.

21. Thank for your attention! 谢谢！

22. PHOBOS , nucl-ex/0510042v1, nucl-ex/0604017v1

24. single jets dijets Surviving jets contributing to hadron at RHIC b=0 AuAuat RHIC Only vertical surface emission for single hadron Tangential surface emission + punch-through for dihadron

25. 2) Suppression factors vs centrality single hadron 0-5% 0-10% 10-20% 20-30% 30-40% 40-50% 50-60% 60-70% 70-80%

26. the formula of spectra inAA nuclear modification factor

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

28. The dihadron azimuthal distributions

29. The ratio between the yield/trigger in AA and in pp:

30. for

31. jets