The objective of this research is to provide important experimental information on the fundamental structure of both free protons and neutrons (nucleons) and those bound inside the atomic nucleus. When scattering leptons from nucleons with large momentum transfer the process can be described within perturbative QCD in which the scattering takes place on an asymptotically free quark with a well defined longitudinal momentum distribution. On the other hand, the quarks are confined inside mesons and baryons, and at low momentum transfer it is these composite particles which are the effective degrees of freedom. One focus of this research is on better understanding the transition between these regimes. In particular, this grant will support work on a precision determination of the magnetic elastic form factor of the proton to large momentum transfer to study the transition to perturbative scaling, in addition to a measurement of the F_2 structure function of the proton and deuteron at large Bjorken-x, for which most of the nucleon momentum is carried by a single valence quark. The former experiment will be performed in Jefferson Lab experimental Hall A and the latter in Hall C.
In addition, this research will study the modification of the nucleons in the nuclear medium, for which no generally accepted physics model currently exists. While many studies of the ratio of structure functions measured in nuclei to those on the deuteron have been performed in electron and muon scattering, practically no experimental data exists for neutrino scattering. Such data would provide important tests of models of medium modifications and will be the focus of the upcoming MINERvA medium energy beam run, while the continuing analysis of the successfully concluded low energy run is primarily focused on elastic scattering and resonance production.
From a broader perspective, this project aims to further elucidate the structure of the nuclear constituents of ordinary matter via new experimental data. While, Quantum Chromodynamics (QCD) has been accepted as the theory of the strong interaction, which is responsible for confining the constituent quarks and gluons into the composite hadrons which make up ordinary matter, many questions of the resulting structure still remain.These studies will be performed with complementary probes via the electromagnetic interaction, utilizing the electron beam at Jefferson Lab, and the weak interaction, utilizing a neutrino beam in the MINERvA experiment at Fermilab.
Both Jefferson Lab experiments are expected to be among the first performed after the energy upgrade of the accelerator. This will leverage the significant expertise of this group to the commissioning of both Hall A and Hall C in support of these experiments, which will also broadly support the larger Jefferson Lab nuclear physics program. It is expected that this research program will also address a critical need in the training of the next generation of researchers in physics, where African-Americans and women are both significantly under-represented.
