Parton Transport via Transverse and Longitudinal Scattering in Dense   Media
  The effect of multiple scatterings on the propagation of hard partonic jets in a dense nuclear medium is studied in the framework of deep-inelastic scattering (DIS) off a large nucleus. Power counting arguments based on the Glauber improved Soft-Collinear-Effective-Theory are used to identify the class of leading power corrections to the process of a single parton traversing the extended medium without emission. It turns out that the effect of longitudinal drag and diffusion (often referred to as straggling) is as important as transverse scattering, when relying solely on power counting arguments. With the inclusion of momentum exchanges in both transverse and longitudinal directions between the traversing hard parton and the constituents of the medium, we derive a differential equation for the time (or distance) evolution of the hard parton momentum distribution. Keeping up to the second order in a momentum gradient expansion, this equation describes in-medium evolution of hard jets which experience longitudinal drag and diffusion plus the transverse broadening caused by multiple scatterings from the medium. 
Guang-You Qin, Abhijit Majumder
hep-ph nucl-th