In Quantum Chromodynamics, the theory of the strong interactions, the nucleon emerges as a relativistic strongly interacting system of quarks and gluons (partons). QCD factorization theorems provide a reliable theoretical formalism that enables one to connect hadron observables to their confined parton degrees of freedom. With the use of collinear factorization, experiments have provided a well documented one-dimensional (longitudinal momentum) snapshot of the nucleon’s internal structure in terms of universal collinear parton distribution functions.
In more recent years, new data sensitive to the transverse momentum partonic structure of hadrons are now available worldwide; among them the COMPASS experiment at CERN (from the earlier HERMES experiment at DESY), RHIC at BNL, Drell-Yan experiments at Fermi Lab, and SIDIS experiments at JLAB. In turn, theoretical advances enabled a paradigm shift in our picture of the partonic structure of the nucleon, which is now three dimensional in momentum space (or one dimension longitudinal, and 2 Fourier spatial degrees of freedom). This more detailed structure is encoded in the transverse momentum dependent parton distribution functions (TMD PDFs). I will present new work that relates TMD and collinear QCD factorization in a generalized framework. This work is preformed in the spirit of providing a quantitative link between measurements and the 3-D partonic structure of the nucleon.