Speaker: D. W. Sivers (Portland Physics Institute/U-M)
The proton and its isospin partner, the neutron, present unique challenges in quantum field theory. Long considered “elementary” particles they have, instead, been revealed to be complex, composite systems of quarks and gluons. This structural complexity provides a fulcrum for the generation of complexity in larger systems. The structure of the nucleon plays its role in stellar evolution and allows the formation of complex nuclei in stellar cores. When liberated by supernova events, the dense spectrum of heavy nuclei provides the base for a broad range of chemical bonds that leads to diverse states of matter. In the serious study of the underlying structure of the proton and neutron, parity-conserving spin observables play a unique role. In any quantum system, Planck’s constant, not only represents a unit of angular momentum, it also provides the unit for measurement of complexity and information. With access to spin-dependent observables, we therefore can study the complexity of the proton associated with confinement and chiral symmetry on unit of Planck's constant at a time. This talk discusses the current understanding of perturbative and nonperturbative tools in QCD used to extract such information from both exclusive and inclusive scattering processes.