Nonuniversality of transverse Coulomb exchange at small x

Within an explicit scalar QED model we compare, at fixed x<<1, the leading-twist Kperpendicular-dependent 'quark' distribution fq(x,Kperpendicular) probed in deep inelastic scattering and Drell-Yan production and show that the model is consistent with the universality of fq(x,Kperpendicular). The extension of the model from the aligned jet to the symmetric kinematical regime reveals interesting properties of the physics of Coulomb rescatterings when comparing DIS and DY processes. At small x the transverse momentum induced by multiple scattering on a single center is process dependent, as well as the transverse momentum broadening occurring in collisions on a finite size nuclear target