1. A NLO Analysis on Fragility of Dihadron Tomography in High Energy AA Collisions I.Introduction II.Numerical analysis on single hadron and dihadron production III.Conclusions Han-Zhong Zhang Institute of Particle Physics, Huazhong Normal University, China Co-authors: J. Owens E. Wang X.-N. Wang Quark Matter 2006Nov. 18, 2006

2. I. Introduction Hard Probe Signal of QGP in RHIC and LHC Jet quenching: Induced by multiple scattering in QGP medium, a parton jet will radiate gluon and lose its energy. Han-Zhong Zhang IOPPQM 2006 Shanghai 2 hadrons q q leading particle leading particle N-N collision hadrons q q Leading particle suppressed leading particle suppressed A-A collision

3. 3 Jet quenching in 2→2 processes LO analysis of jet quenching in AA: 2→2 processes (tree level) A factor K=1.5-2 was put by hand to account for higher order corrections Han-Zhong Zhang IOPPQM 2006 Shanghai

4. 4 Jet quenching in 2→3 processes Motivation : 1) contribution for higher order correction? 2) find a robust probe of dense matter 2→3 processes (tree level) NLO (Next to Leading Order ) corrections: One-loop corrections (Jeff. Owens, PRD65(2002)034011; B.W. Harris and J. Owens, PRD65(2002)094032) K is absent Han-Zhong Zhang IOPPQM 2006 Shanghai

5. Jet Quenching effects lead to the modification of FF Modified Fragmentation Function (FF) 5 KKP (X. -N. Wang, PRC70(2004)031901) and the averaged scattering number, where It determines the thickness of the outer corona where a parton jet survives in the overlapped region. Han-Zhong Zhang IOPPQM 2006 Shanghai

6. In 1-demension expanding medium, the total energy loss: The energy loss with detailed balance: (Enke Wang and Xin-Nian Wang, PRL87(2001)142301) 6 An energy loss parameter proportional to the initial gluon density Han-Zhong Zhang IOPPQM 2006 Shanghai

7. II. Numerical analysis on single hadron and dihadron production 7 1) fix scales and energy loss parameter 2) the centrality dependent of the suppression factor 3) hadron contour plot 4) fragility of single and dihadron tomography Han-Zhong Zhang IOPPQM 2006 Shanghai

8. p-p data at 200GeV are used to fix scales, The invariant p_T spectra of single hadron 8 Han-Zhong Zhang IOPPQM 2006 Shanghai

9. 0-10% AuAu data at 200GeV are used to fix the energy loss parameter (proportional to the initial gluon density): 9 Han-Zhong Zhang IOPPQM 2006 Shanghai

10. 10 Centrality Dependence Han-Zhong Zhang IOPPQM 2006 Shanghai

11. 11 y x Single hadron Color strength = single hadron yield from partons in the square parton jet emission surface completely suppressed Single hadron is dominated by surface emission corona thickness Han-Zhong Zhang IOPPQM 2006 Shanghai

12. 12 1.68 Similar to the study by K. J. Eskola, H. Honkanen, C. A. Salgado, U. A. Wiedemann, NPA747 (2005) 511-529 is a fragile probe of dense matter. loses its effectiveness as a good probe of dense matter Han-Zhong Zhang IOPPQM 2006 Shanghai

13. Fit dAu data by pp result to fix scales, Invariant mass No jet quenching in d+Au, 13 of dihadron in Au+Au collisions 0.3 Han-Zhong Zhang IOPPQM 2006 Shanghai

14. 14 If no jet quen- ching, Han-Zhong Zhang IOPPQM 2006 Shanghai

15. The ratio between the yield/trigger in AA and in pp: If no jet quen- ching, 15 PRL95(2005)152301 0.3 Han-Zhong Zhang IOPPQM 2006 Shanghai

16. partonic di-jet N S tangential 16 y x triggered hadron associated hadron Color strength = dihadron yield from partons in the square Dihadron is from surface emission + punch-through jets punch-through jets 25% left Han-Zhong Zhang IOPPQM 2006 Shanghai

17. 17 1.68 is a robust probe of dense matter. at 200GeV Trigger: 8GeV at RHIC Han-Zhong Zhang IOPPQM 2006 Shanghai

18. 18 is a robust probe of dense matter. at 5.5TeV Trigger: 20GeV at LHC Han-Zhong Zhang IOPPQM 2006 Shanghai LHC

19. III. Conclusions 19 Because of the additional 2→3 processes, NLO contributions behave with stronger quenching effect than LO contributions: Because of the stronger quenching effects, the single hadron is dominated by surface emission; the dihadron is from surface emission + punch-through jets. The dihadron is more sensitive to the initial gluon density than the single hadron. When becomes fragile in higher energy AA, is a robust probe of dense matter. Without inputing K factor by hand, NLO results fit data well. 1) 2) 3) Han-Zhong Zhang IOPPQM 2006 Shanghai

20. Thank for your attention! 谢谢！ 20 Han-Zhong Zhang IOPPQM 2006 Shanghai

21. is the differential 2-body or 3-body phase space element The inclusive cross sections for single hadron production: The inclusive cross sections for dihadron production: is the squared matrix elements Han-Zhong Zhang IOPPQM 2006 Shanghai

22. Hard sphere model Han-Zhong Zhang IOPPQM 2006 Shanghai

23. nuclear modification factor the formula of spectra in AA Han-Zhong Zhang IOPPQM 2006 Shanghai

24. (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) Han-Zhong Zhang IOPPQM 2006 Shanghai

25. Nuclear shadowing effects only in small p T region So in large p T, medium effects only come from Jet Quenching !!! Han-Zhong Zhang IOPPQM 2006 Shanghai

26. Invariant mass: How to fix scales: If no medium effects, (X. –N. Wang, PLB 595(2004)165 Han-Zhong Zhang IOPPQM 2006 Shanghai

27. The dihadron azimuthal distributions Han-Zhong Zhang IOPPQM 2006 Shanghai

28. There are much more punch-through jets in higher energy AA collisions, increases while decreases with collision energy. RHICLHC Han-Zhong Zhang IOPPQM 2006 Shanghai

29. is a robust probe of dense matter. at 5.5TeV Trigger: 20GeV at LHC Han-Zhong Zhang IOPPQM 2006 Shanghai