Experimental Studies of the QCD Structure of the Neutron

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One of the most successful theories in all of science is the Standard Model of particle physics. It describes the fundamental interactions of the sub-atomic particles that make up the visible universe. Within the Standard Model, the Strong Force is described by Quantum Chromodynamics (QCD) and this force governs the interaction between the constituent particles making up the protons and neutrons (collectively "nucleons") in the nucleus of ordinary matter. While QCD has been remarkably successful in explaining many aspects of nucleon structure, many questions still remain. Understanding how the fundamental force between the constituent particles (quarks and gluons) leads to the structure of the protons and neutrons is one of the overarching ambitions of modern nuclear physics. Over the past several decades, one of the most powerful experimental tools for nucleon structure studies has been the scattering of fast electrons from nucleons inside atomic nuclei. This project will support an experimental program of electron scattering to study the fundamental structure of the neutron and proton in the case when an electron is scattered from a single "valence" quark. This case is of particular interest as there are some definite mathematical predictions for the ratio of the up to down quark distributions, and precise measurements would test our understanding of the QCD theory. In addition, this research program will address a critical need for training the next generation of physicists and provide science training to historically underrepresented groups, including women and African-Americans working directly on the project. The presence of highly visible, leading edge research on the campus of a minority institution provides students with exposure to science that might not otherwise be accessible. The research program will be accomplished via two complementary experiments carried out with the electron beam at the Thomas Jefferson National Accelerator Facility (JLab). The Hampton group has a leadership role in both experiments, and each experiment will be the dissertation topic for a Hampton Ph.D. student. The first experiment will measure the nearly free neutron structure function and the ratio of down to up quark distributions via the method of spectator proton tagging from a deuterium target. The Hampton group has responsibility for design, construction, and operation of the recoil proton detector in addition to contributions to the data analysis and simulation. The second experiment took data in 2018 in Hall C to measure the inclusive proton and deuteron F2 structure functions at large Bjorken-x. The Hampton group participated in the data analysis and simulation efforts, as well as systematic studies of the new SHMS spectrometer in Hall C.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.