Colloquia

The task of the field of nuclear physics called femtography is to image the internal structure of strongly interacting particles, from single protons and neutrons to atomic nuclei. Protons and neutrons are composed of quarks and gluons, but the precise spatial arrangement of the two valence up quarks and one valence down quark, along with the sea quarks and gluons that contribute half of the momentum, remains unknown.  A compelling method for deriving dynamical information about the internal structure of the proton is through the use of generalized parton distributions (GPDs).  Two-dimensional Fourier transforms of GPDs provide insight into matter, charge, and radial distributions of the quarks and gluons inside the nucleon.  We present an explicit calculation of such transforms in a spectator model framework using parametric analytic forms of GPDs, originally constrained using deeply virtual Compton scattering and lattice QCD data.  We compare the valence quarks to the gluon distribution through, i.a., average radii, a notion of distance inside the nucleon, and we present a novel result for the radius of the gluon density.