OVERVIEW

3D parton distribution functions have been widely recognized as key objects to gain new insights on the QCD-dynamics inside hadrons. This includes generalized parton distribution functions (GPDs) containing information on the transverse spatial distributions of partons, and transverse momentum dependent distribution functions (TMDs) containing the complementary momentum space information.

In recent years a significant amount of data on spin-azimuthal observables from polarized lepton-nucleon scattering, polarized hadron-hadron collisions and electron-positron annihilations has been provided by several collaborations, including HERMES, COMPASS, BELLE, BaBar, Halls A, B and C at JLab and PHENIX and STAR at RHIC (BNL). After the first few years of running of JLab12 and the upcoming polarized pp runs at RHIC, a significantly greater set of data will be available. Although the interest in TMDs and GPDs has grown enormously we are still in need of fresh theoretical and phenomenological ideas.

The development of reliable and model independent techniques is required, especially for the extraction of TMDs and fragmentation functions from the experimental observables. A precise mapping of the 3D nucleon structure and a detailed flavor decomposition of 3D parton distribution functions are the ultimate goals.

The key questions in the field of the transverse parton structure of hadrons to be addressed by the workshop include:

• QCD issues associated with the 3D structure
• Framework for the extraction of 3D parton distributions
• MC generators for global analysis of TMDs and GPDs
• Phenomenology of 3D parton distribution and fragmentation functions
• Factorization issues in hadron production from hadronic reactions