Session Q03: Modern 3D Structure of Hadrons

Transverse-momentum dependent proton structure

The status of measurements aiming to access the transverse-momentum dependent (TMD) partonic structure of the proton will be given. These TMD data provide insight into transverse nucleon and quark/gluon (parton) spin, parton transverse momenta, and their respective correlations. The complementary TMD data collected in proton-proton collisions (RHIC), semi-inclusive deep-inelastic scattering (DESY, Jefferson Lab, CERN), Drell-Yan production (CERN, Fermilab) and electron-positron annihilation (RIKEN) allow accessing TMD parton distribution functions (PDFs) and fragmentation functions (FFs), which provide a possible pathway to mapping multi-dimensional nucleon structure.  

    

TMD theory and phenomenology

The announcement of the Electron-Ion Collider (EIC) has kindled an era of rapid developements in our theoretical understanding of TMDs. In the past year, theorists have presented evolution equations of TMDs at four loops. As a consequence, phenomenologists have performed the highest precision extraction of the unpolarized TMDs. These studies have been complemented by an amitious theoretical search for processes at the EIC which probe novel aspects of the spin and gluon structure of the proton. Nevertheless, theorists have just scratched the surface on the exciting TMD physics that can be uncovered by the EIC. In this talk, I'll introduce several promising subjects in TMD theory and phenomenology including: TMDs at sub-leading power, which serves as a new direction for precision determination of the TMD structure of hadrons, TMDs in a nuclear medium, which allows us to address how the nuclear medium alters the structure of hadrons, TMDs at small x and GCG physics, and energy-energy correlators and the nucleon energy-energy correlator.   

Lattice QCD on 3D Structure

The transverse-momentum-dependent parton distributions (TMDs) provide a 3D imaging of the proton in high-energy scattering experiments such as those at Fermilab, Jefferson Lab, RHIC, LHC and the future Electron-Ion Collider. Recent years have seen much progress in the global fitting of TMDs from experiments, and along with that is a lattice QCD program aiming at first-principles calculation of these quantities, especially in the non-perturbative domain. Thanks to the breakthroughs in theory, notably the large-momentum effective theory (LaMET), it is now feasible to calculate both quark and gluon TMDs from a set of lattice TMDs through effective theory matching. In this talk, I will introduce the LaMET framework for TMD calculation, and review the recent progress in calculating the Collins-Soper evolution kernel for TMD evolution, as well as the soft factor and full TMDs.