1. Zhangbu Xu, USTC 2008 1 Jet Quenching at RHIC 喷注淬灭 1.Basic properties of QCD relevant to us 2.Fragmentation Function in e + e - and p+p 3.New Measurements at RHIC 4.Compile RHIC data on jet chemistry 5.Extract effective gluon Color Charge at RHIC 6.Other unique features of QCD jet quenching 7.Conclusion and Outlook

2. Zhangbu Xu, USTC 2008 2 Fundamentals of QCD relevant to our field T.D. Lee, 1995 Quark Confinement 夸克禁锢 Symmetry Breaking 对称破缺 Gluons carry color-charge Asymptotic Freedom

3. Zhangbu Xu, USTC 2008 3 Color Factors QCD : For SU(3) : N c = 3 C A = 3, C F = 4/3 C F ~ strength of a gluon coupling to a quark C A ~ strength of the gluon self coupling T F ~ strength of gluon splitting into a quark pair C A /C F =9/4  s 藕合常数

4. Zhangbu Xu, USTC 2008 4 Energy Loss and QCD Experimentally observable (of E loss ) related to basic ingredient of QCD - Gauge Group through Color Factors Or extracting an effective Color Factor R. Baier et al., NPB 483 (1997) 291 M. Gyulassy et al., PRL 85 (2000) 5535 S. Wicks et al, nucl-th/0512076 hard parton path length L One mechanism of energy loss : Medium induced gluon radiation EgEg EqEq ~ 9/4 2 L C E s   ^  C

5. Features of QCD energy loss Color factor and coupling constant Pathlength L 2 dependence Deadcone Jet chemistry and Jet Conversion Mach Cone Zhangbu Xu, USTC 2008 5 1982: J. D. Bjoken: Fermilab-pub-82/59-THY Energy loss in elastic scattering 1992/1995: X.-N. Wang, M. Gyulassy: PRL68(92) 148, PRD45 (92)844, NPB420(94)583, PRD51(95)3436 Energy loss is dominated by gluon radiation 1995/1997: BDMPS (R. Baier, Yu. L. Dokshitzer, A. Mueller, S. Peigue, D.Schiff) :PLB345(95) 277, NPB478(96)577,NPB483(97)291,NPB484(97)265 Gluon multiple scattering and gluon radiation 2000: GLV(M. Gyulassy, P. Levai, I. Vitev): PRL85(00)5535, NPB594(01)371 U. Wiedemann: NPB588(2000)303 Opacity expansion 2001/2002: E. Wang, X.-N. Wang: PRL87(01)142301, PRL89(02)162301 Detailed Balance; Jet Tomography 2001/2009 Y. Dokshitzer & D. Kharzeev PLB 519(2001)199; S. Wicks et al, nucl-th/0512076

6. Zhangbu Xu, USTC 2008 6 Consequence of C A /C F =9/4 in A+A Other models: S. Wicks, I. Vitev, QM08 WHDG, arXiv:nucl-th/0512076 (AA/pp) q/g~=9/4 QGP 内高能部分子能损前后 的空间分布

7. Zhangbu Xu, USTC 2008 7 Processes in hadron-hadron collisions PYTHIA provided by Adam Kocoloski gg qq gq PDF  Parton 2->2  Fragmentation functions  部分子分布函数 (PDF)  部分子作用截面  碎裂函数

8. Zhangbu Xu, USTC 2008 8 我们需要的量 1. 核子内部分子分布函数 (PDF) 理论函数 (CTEQ6M) 拟合实验数据 (e+p) 2. 部分子作用截面和出射动量 二次展开的微挠色动力学 (NLO pQCD) 3. 碎裂函数 ( 喷注中强子的分布 ) 只取喷注中大动量的单个强子 没有重建原始部分子 理论函数 (DSS) 拟合实验数据 (e + e -,e+p,p+p) 4. 部分子在 QGP 中的能损机制

9. Zhangbu Xu, USTC 2008 9 Fragmentation Functions Will these ingredients be sufficient for p+p collisions? How will p+p collisions provide additional information for our understanding of QCD and for model developments What will be modified in A+A collisions 1.FF 2.Running of  S 3.Effective Color Charge factor 喷注中强子的分布

10. Zhangbu Xu, USTC 2008 10 PID at high-p T (where do we start?) My talk: p T >5 GeV/c Where it begins

11. Zhangbu Xu, USTC 2008 11 Sources of high p T hadrons : quarks or gluons At high p T range measured : Large gluon contribution (~ 90%) to produced baryons Substantial quark contribution (~ 40%) to produced mesons STAR : PLB 637 (2006) 161S. Albino et al, NPB 725 (2005) 181 N g (i)/ (N g (i) + N q (i)); i = , K, p… B. Mohanty (for STAR) nucl-ex/0705.9053 L. Ruan (for STAR) nucl-ex/0701070 and WWND

12. Zhangbu Xu, USTC 2008 12 Global Fit Daniel de Florian, Rodolfo Sassot and Marco Stratmann arXiv: 0707.1506 [hep-ph]; Phys.Rev.D76:074033,2007. DSS Fragmentation Functions –provided by W. Vogelsang In principle, allow to separate quark-to-proton and anti-quark-to-proton fragmentation functions The best constraint on the gluon fragmentation function D g p at large values of z currently available.

13. Zhangbu Xu, USTC 2008 13 Extend Charged hadron spectra! P. Fachini, QM08 Y.C. Xu, DNP07

14. Zhangbu Xu, USTC 2008 14 Comparison with pQCD 1.Clear flavor dependence 2.DSS NLO overpredicts pbar yield 3.Best constraint on gluon/quark-to-proton fragmentation functions at high z Not all models are equal!

15. Zhangbu Xu, USTC 2008 15 Quark vs gluon from hadron suppression X.N. Wang and X.F. Guo, NPA 696(2001)788 T. Renk and K. Eskola, PRC 76 (2007)027901 W. Liu, C.M. Ko, B.W. Zhang, nucl-th/0607047 PRL 97, 152301 (2006) STAR Preliminary No sign of stronger gluon energy loss in p/  or p/p ratios Need good understanding of how quarks and gluons turn into hadrons STAR, B. Mohanty STAR, P. Fachini Curves: X-N. Wang et al PRC70(2004) 031901 质子和介子在 QGP 强子压底前后的比值

16. Zhangbu Xu, USTC 2008 16 Thermal distribution among hadrons Statistical Mechanics describes the relative particle abundances This happens at the phase boundary (T=165+-10MeV) STAR whitepaper Low-p T integrated yields 强子的热统分布 : 温度和化学势

17. Zhangbu Xu, USTC 2008 17 Jet Chemistry in p+p p T >5 GeV/c 4<pT<5 GeV/c 高动量强子化学分布  强子来源和 QGP 作用下的变化

18. Zhangbu Xu, USTC 2008 18 Effective Color Factor a 1  E q +b 1 dE g ----------------- = a 2  E q +b 2  E g 10%+90%C ----------------- = R AA (  p/  ) 60%+40%C 100% ----------------- = R AA (e/  ) 60%+40%C Simple Algebra:

19. Zhangbu Xu, USTC 2008 19 Extract effective Color Factors ALEPH : ZPC 76 (1997) 1 OPAL :EJPC 20 (2001) 601 SU(3) is the gauge group for QCD  S = 0.119

20. Zhangbu Xu, USTC 2008 20 Convert to Effective C A /C F hard parton path length L hard parton path length L 20%+80%C ----------------- = R AA (K S 0 /  ) 60%+40%C Conversion probability can be absorbed into C: <= W. Liu, R.J. Fries, arXiv:0801.0453[nucl-th]

21. Zhangbu Xu, USTC 2008 21 Constraints on Opacity (QGP 透明度 ) Look at data in a quantitative way Geometry and evolution, dE/dx model How the gluon and quark compositions change with dE/dx? Different PID and global constraints on initial jet composition PHENIX: WHDG R AA (C,  E q,p T,FF)

22. Zhangbu Xu, USTC 2008 22 Outlook - Energy Dependence Similar E loss for quarks and gluons QCD type (color charge effect) E loss Probing quark dominated jet production at lower energy to gluon dominated jet production at higher energy Heavy-Flavor tag  +jet pbar-pbar I AA (T. Renk) Wang et al., PRC 58 (1998) 2321 Wang et al., PRC 71 (2005) 014903 B. Mohanty, ISMD2007

23. Zhangbu Xu, USTC 2008 23 Advantage of Di-hadron Correlations 双强子关联 y (fm) x (fm) Less surface bias Single Di-hadron y (fm) x (fm) Limited sensitivity of R AA to P(  E,E) T. Renk, PRC 74 (2006) 034906 T. Renk and Eskola,hep-ph/0610059 Di-hadron correlations more robust probes of initial density ~ H. Zhong et al., PRL 97 (2006) 252001  2 IAA  2 RAA

24. Zhangbu Xu, USTC 2008 24 光子无能损, 可用来标定与其关联的喷注的原初能量 Beam axis 180° BEMC TPC  光子 — 强子关联 No track with p>3GeV/c points to the trigger tower 00 2 Leading particle Study the particles distribution in fractional energy of  ’s energy Use Transverse Shower Profile for  /  0 identification.

25. Zhangbu Xu, USTC 2008 25 光子 — 强子角关联的试验分布  -rich sample versus  0 -rich sample o The  -rich sample has lower near-side yield than  0.

26. Zhangbu Xu, USTC 2008 26 E loss probability distribution :  -hadron correlation Provides constraints on E loss probability distributions Possibly gives full accounting of jet energy loss Jet Prompt  1 st measurement of away-side  -h correlations Suppression similar level as inclusives in central collisions Note : E jet = E  X.-N. Wang et al PRL 77(1996)231

27. Zhangbu Xu, USTC 2008 27 Conclusions QED  FQHE(perfect fluid)  Chern-Simon A large dataset extended to higher momentum with many identified particles in p+p and A+A collisions Effective gluon color charge factor<9/4 Modeling flavor and color charge effects R AA (C,  Eq,p T,FF) QCD  sQGP (perfect Liquid)  ?

28. Zhangbu Xu, USTC 2008 28 作业题 I 计算喷注淬灭能损后 ( 反质子 / 介子 ) 的比值 假设  p/  in p+p,  p 100% from gluon,  30% from gluon, 70% from quark 而且认为 SU(3) (pQCD) 可适用 1.>1 2.[0.25,1] 3.[0.01,0.25] 4.<0.01

29. Zhangbu Xu, USTC 2008 29 作业题 II 2 ）喷注淬灭能损后的能量跑哪儿去？ 3 ）喷注淬灭能损（ dE/dx) 和 带电粒子穿过探测 器的能损比较。

30. Zhangbu Xu, USTC 2008 30 Nuclear Modification Factor P. Fachini (STAR) 1.Same R AA for , ,  2.Different R AA for pbar,p,Ks, e(NPE)

31. Zhangbu Xu, USTC 2008 31 Current Observations in STAR Away side yield modification What does these features reveal about the medium ? Parton E loss High p T suppression STAR : PLB 655 (2007) 104 STAR : PRL 97 (2006) 152301 STAR : PRL 91 (2003) 072304 Reappearance of di-jets STAR : PRL 97 (2006) 162301 p Tlp : 4 - 6 GeV/c p Tasoc : 2 GeV/c - p Tlp Away side shape modification d+Au Enhanced correlated yield at large  on near side Medium response STAR : J. Putschke, QM2006 STAR : M. J. Horner, QM2006 2.5 < p T trig < 4 GeV/c 1< p T assoc < 2.5 GeV/c p T trig =3-6 GeV/c, 2 GeV/c <p T assoc < p T trig Au+Au STAR: PRL 95 (2005) 152301 J.G. Ulery, QM 2005