1. To Those Who Perished in the 5.12 Earth Quake in China

2. Xin-Nian Wang LBNL 4 Th Electron-Ion Collider Workshop Hampton, May 19-23, 2008 Quark Propagation in a Nuclear Medium

3. Medium Response Function Dynamic System: Photon or dilepton emission J/  suppression QCD Response:Quark-medium scattering

4. Quark Propagation: Jet Quenching & Broadening dE/dx  modified frag. functions hadrons phph parton E D h/a (z)=dN/dz (z=p h /E) Suppression of leading particles Fragmentation Function Angular distribution dN/d 2 k T  jet broadening

5. DIS off a large nucleus Loosely bound nucleus (p +, q - >> binding energy) e-e-

6. Collinear Expansion Collinear expansion: Ward identities

7. Collinear Expansion (cont’d) ‘Twist-2’ unintegrated quark distribution q xp = ‘Twist-3’ unintegrated quark distribution x1px1p q xp

8. TMD (unintegrated) quark distribution Longitudinal gauge link Belitsky, Ji & Yuan’97 Transverse gauge link

9. Transport Operator All in terms of collinear quark-gluon matrix elements Liang, XNW & Zhou’08 Taylor expansion Transport operator

10. Maximal Two-gluon Correlation

11. Nuclear Broadening & Gluon Saturation Quark jet transport parameter Liang, XNW & Zhou’08 Coherence effect  correlation between different nucleons Gluon saturation Kochegov & Mueller’98 McLerran & Venugapolan’95

12. SIDIS off Nuclei e-e- Frag. Func.

13. DGLAP Evolution Splitting function q p k1k1 k2k2 p q

14. Induced gluon emission in twist expansion q Ap xp Ap q x 1 p+k T Collinear expansion: Double scattering

15. LPM Interference Formation time

16. Modified Fragmentation Modified splitting functions Guo & XNW’00 Two-parton correlation:

17. Quadratic Nuclear Size Dependence

18. HERMES data in Au nuclei E. Wang & XNW PRL 2000

19. Energy Dependence

20. Jet quenching in heavy-ion collision Central Au+Au single hadron dihadron in cold nuclei in hot matter

21. Summary Quark transverse momentum distribution can be expressed in term collinear quark-gluon matrix elements quark propagation in nuclei leads to k T broadening  gluon correlation function Jet transport parameter qhat  saturation scale Q sat 2 Modified fragmentation function  qhat~0.01 GeV^2/fm in HERMES at HERA versus qhat~ 1- 2 GeV^2/fm in QGP at RHIC qhat at small x and large Q^2 can reveal gluon dynamics (correlation, saturation) in nuclei