Grant: Subatomic Physics Envelope - Project

<p>One of the central problems of modern physics research concerns our understanding of the building blocks of the atomic nucleus---the protons, neutrons, and other particles (mesons) that bind them. Our conception of these particles has led to the picture that these particles consist of yet more fundamental constituents, the quarks and gluons. While a very good theoretical framework (called Quantum Chromo-Dynamics, or QCD) is able to accurately describe how quarks and gluons interact at extremely high energies (or, equivalently, when the quarks are very close together), it has been very difficult to apply QCD to lower energy (larger distance) phenomena. The paradox is that the increasing complexity of the quark-gluon interaction as they get further apart is critically important to their confinement within the nuclear building blocks, but we cannot perform the QCD calculations necessary to confirm our understanding. The complex quark-gluon interaction is manifested in the rich structure that protons and neutrons have been measured to possess---they can be excited into many different ""excited states"", have unique spatial distributions of internal electric charge and magnetism, and unique responses when probed by electric or magnetic fields. But the exact connection of these observed low-energy structure properties to the underlying theory of QCD is only partly understood. This research project represents a continuation of the collaboration of researchers at three Canadian universities joining efforts to use the experimental facilities at the Institute for Nuclear Physics in Mainz, Germany, to make precision measurements related to hadron structure. The goal of these experiments is to focus on measuring specific hadron structure details that show particular promise of allowing a direct connection to underlying quark/gluon dynamics through comparison to modern QCD-inspired model calculations, and to solutions to QCD done computationally on a ""lattice"". Results from measurements in this project, and from others like it at laboratories throughout the world, provide the tools to make the elusive connection between quark/gluon dynamics and the observed hadron structure.</p>