Probing the Electromagnetic Structure of Hadrons at Jefferson Lab

点击翻译按钮获取中文摘要

During the past century, a revolution has occurred in the understanding of the structure of matter - specifically, in understanding the atomic nucleus. 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") which interact via exchanges of lighter particles called mesons (with the pion being the lightest); 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 upgraded electron beam facility at Jefferson Laboratory in the USA to make precision measurements of proton (and pion) structure. The biggest effort in this project will be the design and construction of a new scintillating-fiber "coordinate detector" to be used for providing precision position and angle measurements of elastically-scattered electrons from the proton in efforts to push studies of the proton's "form" (or structure) to the most extreme limits ever reached.