Nucleon tomography

Abstract

Starting from the interpretation of the nucleon electromagnetic form factors in terms of charge/magnetic density, we illustrate the need and the advantages of a multidimensional exploration of the structure of the nucleon, and in general of hadrons. We introduce new tools, like the Generalized Parton Distributions (GPDs) and the Transverse Momentum Distributions (TMDs), which enable us to explore the dynamics of partons beyond the usual collinear approximation adopted in the QCD analysis of hard processes. We emphasize the possibility of using these tools to address the (orbital) angular momentum of partons, and we highlight the latest results on the partonic decomposition of the nucleon spin. We briefly touch on the possible breaking of universality for a specific category of TMDs; as an example, we describe the Sivers effect as a fundamental test of our understanding of the color force in QCD.