Transverse momentum broadening due to the multiple scattering
  Using the Drell-Yan process in hadron-nucleus collisions and deeply inelastic lepton-nucleus scattering (DIS) as examples, I show that the transverse momentum broadening can be expressed in terms of four-parton correlation functions. I argue that jet broadening in DIS provide an excellent measurement of the four-parton correlation functions and a test of QCD treatment of the multiple scattering. 
Xiaofeng Guo (Columbia University)