Neutron-Deuteron Analyzing Power at Various Energies

With the two-nucleon system fairly well understood, there has been increasing interest in recent years in understanding the three-nucleon system, which behaves quite differently than predicted by models incorporating two-nucleon interactions alone. Improvements to theory exist in the form of preliminary three-nucleon force (3NF) models, and have been largely successful in accounting for the difference between theory and experiment with regard to cross-section data, among other observables. Despite this, none of these 3NF's adequately compensate for the discrepancy between theory and experiment in spin-polarized neutron- and proton-deuteron analyzing power at low energies (below about 50 MeV), leading to what has been called the Three Nucleon Analyzing Power Puzzle (3NAPP). This talk covers some physical and historical background for the 3NAPP, and describes in greater detail efforts at Triangle Universities Nuclear Laboratory (TUNL) to measure neutron-deuteron analyzing power at En = .65, 1.2, and 19 MeV.