Quarks and Color Forces with a Spin
Over the past 50 years, a wealth of information critical to our understanding of subatomic matter was obtained by probing the electromagnetic and spin structure of nucleons through lepton (electron) scattering. The first direct observation that protons are not elementary objects and the discovery that their constituents, dubbed partons, are point-like particles, made use of elastic and deep-inelastic scattering of electrons off protons. With the advent of quantum chromodynamics (QCD), the modern theory of strong interactions, partons were identified as quarks and gluons. Since then an intensive theoretical effort is still underway to appreciate the full consequences of this theory.
More recently, scattering experiments at Jefferson Lab using a 6 GeV polarized electron beam and polarized targets at high luminosity have allowed us to delve deeper into the nucleon structure in the valence quark region. These studies are helping unravel the rich but elusive structure of the building blocks of matter as well as impacting our grasp of the non-perturbative aspects of QCD. Recent measurements of the color electric and magnetic forces acting on quarks will be presented. In the quest to complete our understanding of the nucleon structure and its implications within the framework of QCD, a promising future awaits us with the 12 GeV upgrade of Jefferson Lab and a possible future Electron Ion Collider.