Non-universality of transverse Coulomb exchange at small x
Abstract
Within an explicit scalar QED model we compare, at fixed x << 1, the leading-twist KT-dependent `quark' distribution fq(x, KT) probed in deep inelastic scattering and Drell-Yan production, and show that the model is consistent with the universality of fq(x, KT). 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 <kT2> induced by multiple scattering on a single centre is process dependent, as well as the transverse momentum broadening occurring in collisions on a finite size nuclear target.
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