This award will support the continued efforts of the Hampton University intermediate energy nuclear physics group. This group was formed nearly two decades ago to address a critical need in a science where African-Americans are severely under-represented. Since that time the group has significantly expanded the scientific program, while facilitating the successful careers of a number of minority scientists. The group is recognized for leadership in studies of the structure of the nucleon (proton or neutron), in particular in kinematics where the quarks in the substructure carry a large fraction of the total momentum of the system. Precision measurements of nucleon structure in this regime provide critical information regarding the mysterious transition from a scale where only quarks and gluons matter, to the scale where only nucleons and mesons need to be considered. The group has spearheaded efforts to utilize global data sets for a more comprehensive understanding, and to better model the observed phenomena. The group will continue to focus on electron scattering experiments at the nearby Thomas Jefferson National Accelerator Facility, in particular looking in anticipation to the planned energy upgrade of this laboratory. The group will, as well, broaden to focus on the MINERvA experiment at the Fermi National Accelerator Laboratory. This experiment will use the unique properties of neutrinos, which experience only the weak force, as opposed to the electromagnetic probe provided by an electron beam, and carry a neutral charge, as opposed to the negatively charged electrons. Neutrino scattering is a largely uncharted realm in nucleon structure studies, and promises to provide new insights into the quark-gluon structure of the nucleon. The group is also planning further into the future, investigating the possibilities for nucleon structure studies at the energy frontier of a proposed future new electron-ion collider.
This grant supported experimental research into the fundamental structure of ordinary matter; in particular, the structure of the protons and neutrons which compose the atomic nuclei of ordinary atoms. Understanding this structure is a prerequisite for a full understanding of the world in which we live, and was studied through scattering experiments utilizing beams of both charged electrons and charge-less neutrinos at the Thomas Jefferson National Accelerator Facility (JLab) and the Fermi National Accelerator Laboratory (Fermilab), respectively. The protons and neutrons (collectively nucleons) are known to be composed of the fundamental charged quarks, which are bound within the nucleons by the Strong force. Scattering measurements test our understanding of this structure in terms of the well established underlying theory of the strong interaction, Quantum Chromodynamics (QCD). However, many questions remain regarding this underlying structure. This is due to the fundamental nature of QCD which makes answering such questions via mathematical solutions to QCD exceeding difficult. While computational techniques for studying QCD structure with supercomputers have been steadily improving, such results must be confronted with experimental data where possible. The research supported by this grant has provided substantial new information on the structure of free neutrons via scattering electrons from the simplest composite nucleus of deuterium (one proton and one neutron in a weakly bound state) by utilizing a novel technique called 'Spectator Tagging'. While experimental determinations of neutron structure in terms of quarks has long been hampered by the fact that high density free neutron targets do not exist, this new method provides a powerful tool to access neutron structure to much better precision than previously possible. Of particular interest is the ratio of neutron to proton structure, which provides a unique tool to extract information on the distributions for the individual u-quark and d-quark flavors which make up both protons and neutrons. Two publications resulting from this research have been published in leading journals with the primary results already having been incorporated into a new textbook. Another fundamental aspect of nucleon structure studied by this research program was the modification of this structure in the presence of other nucleons in the nucleus, ie. and investigation of the question ``to what extent is the nucleus not just a collection of individual protons and neutrons and how does the interactions between these particles affect the measured structure.'' This question was investigated with experiments with both electron and neutrino beams and resulting in two Ph.Ds by Hampton University graduate students. A full understanding to this question has been long sought after with many experiments having been performed with electron beams, but with very little experimental data available using neutrino beams. This funding supported the participation of this research group on the MINERvA experiment at Fermilab, which was designed to perform such studies has has thus far resulted in 5 publications in peer reviewed journals. One of the broader impacts of this research program was the development of future scientists from historically underrepresented groups, such as African-Americans and women. Under this award, four students (three women) have earned advanced degrees in Physics at Hampton University working on this research, with three Ph.D.s awarded (one African American) and one Master of Science awarded.
