An Experiment to Measure the Weak Axial-Vector Form Factor, F_A(Q²), using the p(e,n)ν Reaction with Polarized Electrons at Q² = 1 GeV²

Lepton-nucleon elastic scattering, mediated by vector bosons, has provided a wealth of information about the structure of the nucleon through extraction of the electromagnetic form factors over a wide range of negative four-momentum exchange, Q². Like the electromagnetic form factors, the exchange of weakly interacting bosons allows one to extract the axial-vector form factors which similarly provide information about the weak charge structure of the nucleon. For the axial-vector form factor in charged current interactions, F_A(Q²), most data come from neutrino scattering for which few experiments exist; all with limited accuracy.

In this talk I will describe a detailed plan for the first experiment to measure F_A at Q² = 1 GeV² through the reaction p(e,n)ν. In contrast to the neutrino scattering results, this experiment will be the first fully kinematically constrained measurement. The reaction will be identified from background processes several orders of magnitude higher using a time-of-flight spectrometer with resolution below 100 ps. The experiment is designed to run at Jefferson Lab with a polarized electron beam where there exists a large-scale neutron calorimeter and a large acceptance electron/pion veto spectrometer. Data from this experiment will not only be used to shed light on the weak structure of the nucleon, but will also be essential for reducing one of the largest systematic uncertainties in neutrino oscillation experiments.