TRANSVERSE SPIN AND MOMENTUM STRUCTURE OF HADRONS IN QCD

One of the major objectives of nuclear physics research is to understand and quantify how hadrons and nuclei emerge from, and are structured in terms of the fundamental constituents of matter. It is predicted from Quantum Chromodynamics (QCD), the gauge theory of quark and gluon interactions, which in principle describe hadrons and nuclei as bound and ultimately confined state of quarks and gluons (partons), that the internal landscape of hadrons can be determined from deep inelastic scattering experiments. Asymptotic freedom makes it possible to utilize the theoretical formalism of QCD factorization to quantify the partonic structure and dynamics of hadrons from deep inelastic scattering measurements where partons become weakly coupled when hadrons are probed at sufficiently short time and distance scales. QCD factorization predicts that the measured scattering cross sections can be factorized in terms of non-perturbative and perturbative factors. While decades of high-energy experiments have provided data allowing for the high resolution of the 1-dimensional (1-D) longitudinal momentum structure of hadrons, the information on the transverse momentum structure of hadrons is comparatively less well known. Achieving a 3-dimensional (3-D) map of the internal structure of hadrons requires sensitivity to both collinear and transverse parton degrees of freedom. Uncovering the 3-D landscape of hadrons is a major the goal of high energy nuclear physics facilities such as the Relativistic Heavy Ion Collider (RHIC, BNL), the Continuous Electron Beam Accelerator Facility (CBAF, JLAB), the COMPASS and Amber experiments (CERN) and the past HERMES (DESY) Experiments, and the future Electron-Ion Collider (EIC, BNL).