Grant: Subatomic Physics Envelope - Individual

During the past century, a revolution has occurred in the understanding of the structure of matter. We have moved well into examination of the myriad of complexity contained inside atoms - proposed as ""indivisible"" in 1805 by Dalton - from molecular structures, to electron orbitals around a nuclear center, to the structure of the atomic nucleus itself. In 1932, the discovery of the neutron brought acceptance to the idea that the atomic nucleus is composed of elementary particles called neutrons and protons (or ""nucleons""); further, during the 1970's, experimental results made it clear that even these nucleons are individually made of more fundamental particles called quarks and gluons. Modern nuclear physics researchers now strive to gain clear insight into understanding the interactions between these underlying quarks and gluons, and how these interactions give rise to the internal structure properties of nucleons. While a very good theoretical framework (called Quantum Chromo Dynammics, or QCD) exists which can accurately describe how quarks and gluons interact at extremely high energies (or, equivalently, when the quarks are very close together), an unfortunate reality is that this theory of QCD is very difficult to solve/interpret at lower energies (or, at larger distances) because the quark/gluon force gets increasingly complicated as they get further apart. However, this complicated interaction of quarks and gluons is manifest by the rich structure which nucleons have been measured to possess; while it's clear such nucleon structure results from the motion of its internal electrically-charged quarks, the exact connection of the observed low-energy structure of nucleons to the underlying theory of QCD remains one of the central problems of modern physics research. This research proposal will exploit the existing 6-billion-Volt electron beam at Jefferson Laboratory in the USA to make precision measurements of low-energy proton structure, as well as contribute to designing/constructing new scintillating-fiber tracking detectors to be used in studies to push these proton structure measurements up in energy as Jefferson Lab enters a construction phase to increase its electron beam energy to 12-billion-Volts.