RUI: Probing the Structure of Excited Baryons that Decay through the Omega-Meson Channel

Lamar University, Beaumont TX

Investigators

Abstract

The strong force gives rise to the nuclear attractions that bind protons and neutrons, otherwise known as nucleons, together inside the nucleus. Understanding exactly how the strong nuclear force is generated inside the nucleus is one of the greatest intellectual challenges facing nuclear physics today. We do know that the strong force is mediated by the exchange of particles known as gluons, and it is this gluon interaction that accounts for most of the mass of the nucleon. The nucleons themselves are formed of three other particles called 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 or a pi-meson, incident on a nucleon can interact directly with one of the quarks inside, exciting the quark to higher energy, making the nucleon more massive. These excited states exist for the briefest of moments, on the order of a trillionth of a trillionth of a second, and then decay into other particles. The types of particles produced and how they are distributed in space provide key information on the make-up of the nucleon. This award to Lamar University, a Primarily Undergraduate Institution, supports the mentoring of undergraduate students as researchers and their preparation for graduate school and/or industry. Two or three undergraduate students will work onsite at the Thomas Jefferson National Accelerator Facility for ten weeks each summer to assist in hardware and software projects at two of the ongoing experiments at the Laboratory. The training provided for this work includes learning how to set up computer systems, writing efficient software, running detector simulations, and scheduling large-scale computations on a computer cluster like the High Performance Computer Cluster at Lamar University. Through their hands-on experience, the undergraduate students will learn the nuances and intricacies of how detectors actually work. Having good hardware skills will give profound insight into the reliability of the final results from data analysis, skills that are highly sought after by graduate schools as well as by industries that deal with big data and data analytics. The students will also learn the soft skills of time management and the overall importance of working together in a team. This award supports the study of the fundamental properties and structure of nucleons through using a beam of linearly-polarized photons, polarized electrons and pions (π+/π–) at Jefferson Lab (USA), ELSA (Germany), and J-PARC (Japan). 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. The PI and his group will seek 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 group aims to understand the emergent behavior and structure from assemblies of quarks and gluons. In the case at JLab and ELSA, the probe for these studies will be the omega meson. There is great discovery potential in probing the structure of N* resonances 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 Q2 for the electromagnetic channels, which is needed to understand the emergence of hadron mass. The PI will use a coupled-channel approach to the pion-beam data to ascertain and assist in amplitude analysis for the two-pion decay channel, which is further necessary for understanding the emergence of hadron mass. 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.