To Those Who Perished in the 5.12 Earth Quake in China
Xin-Nian Wang LBNL 4 Th Electron-Ion Collider Workshop Hampton, May 19-23, 2008 Quark Propagation in a Nuclear Medium
Medium Response Function Dynamic System: Photon or dilepton emission J/ suppression QCD Response:Quark-medium scattering
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
DIS off a large nucleus Loosely bound nucleus (p +, q - >> binding energy) e-e-
Collinear Expansion Collinear expansion: Ward identities
Collinear Expansion (cont’d) ‘Twist-2’ unintegrated quark distribution q xp = ‘Twist-3’ unintegrated quark distribution x1px1p q xp
TMD (unintegrated) quark distribution Longitudinal gauge link Belitsky, Ji & Yuan’97 Transverse gauge link
Transport Operator All in terms of collinear quark-gluon matrix elements Liang, XNW & Zhou’08 Taylor expansion Transport operator
Maximal Two-gluon Correlation
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
SIDIS off Nuclei e-e- Frag. Func.
DGLAP Evolution Splitting function q p k1k1 k2k2 p q
Induced gluon emission in twist expansion q Ap xp Ap q x 1 p+k T Collinear expansion: Double scattering
LPM Interference Formation time
Modified Fragmentation Modified splitting functions Guo & XNW’00 Two-parton correlation:
Quadratic Nuclear Size Dependence
HERMES data in Au nuclei E. Wang & XNW PRL 2000
Energy Dependence
Jet quenching in heavy-ion collision Central Au+Au single hadron dihadron in cold nuclei in hot matter
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