RUI: Probing the Structure of Nucleons in Omega Meson Electroproduction

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Understanding exactly how the strong force is generated inside the nucleus is one of the greatest intellectual challenges facing nuclear physicists today. The strong force gives rise to the nuclear forces that bind protons and neutrons together inside the nucleus. The strong force is mediated by the exchange of particles known as gluons. It is this gluon interaction that accounts for most of mass of the nucleon. The nucleon is the general term for either a proton or a neutron. Nucleons are formed of three valence quarks embedded in a frothing sea of gluons. Our knowledge of how protons and neutrons are constructed from their quark and gluon constituents, however, is rudimentary at best. An energetic particle, such as an electron, incident on a nucleon can interact directly with one of the valence quarks inside, causing the quark to undergo a flip in spin or endowing the quark with an orbital or radial excitation. With a quark in a higher energy state, the excited nucleon becomes more massive. These excited states are called nucleon resonances (N*s) and exist for the briefest of moments – on the order of a trillionth of a trillionth of a second (10−24 s), and thence will decay into other particles. The types of particles produced and how they are distributed in space provides key information on the make-up of the proton. Lamar University is a Primarily Undergraduate Institution. Over the course of the past two decades, the PI has established a strong record of involving undergraduate students in his research program, and that practice will continue with support from this award. These fundamental measurements on understanding nucleon resonances at Jefferson Lab (Newport News, Virginia) and at ELSA (Bonn, Germany), along with the strong educational focus of this award, are in keeping with the key objectives of the Nuclear Science Advisory Committee’s 2015 Long-Range Plan and thereby serve the national interest.This research program is a study of the fundamental properties and structure of nucleons by using a beam of linearly-polarized photons and/or polarized electrons at Jefferson Lab and at ELSA. The strong nuclear interaction is responsible for phenomena over a large distance scale from the binding of quarks by gluons, the combinations of quarks into colorless hadrons, the binding of nucleons into nuclei, and the collective behavior of large nuclei. This research group seeks answers to questions such as how valence quarks self-assemble when sea quark and gluon contributions are minimal, the nature of how gluons attach to quarks to increase the mass of current quarks to that of constituent quarks, and how quarks resonate inside the nucleon to form excited assemblies of quarks. The PI and his group of undergraduate students aim to understand the emergent behavior and structure from assemblies of quarks and gluons. The probe for these studies will be the omega meson. There is great discovery potential in probing the structure of N*s through the clean and unambiguous signal of the omega meson. Moreover, there is a significant dearth of data of baryon resonances decaying through the omega mode as a function of momentum transfer.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.