Three-nucleon experiments and 2S defects

Supported by the results of recent theoretical calculations of nucleon-deuteron scattering, it is suggested that most parts of the calculated three-nucleon scattering and breakup amplitudes are model-independent at low energies and, furthermore, that the $^{2}S$-state amplitudes are the important exception to this rule. On the basis of the assumption that it is only differences between theoretical and physical $^{2}S$ amplitudes which will remain substantial as calculations improve, a new approach to the experimental three-nucleon problem is proposed. According to this approach, experiments would be chosen on the basis of the sensitivity to $^{2}S$ amplitudes and would be analyzed by using theoretical predictions for the amplitudes and empirically adjusted $^{2}S$ defects. Experiments expected to be sensitive to the $^{2}S$ amplitudes are discussed including angular distributions, spin-correlation measurement, and experiments of the triple-scattering type. Formulas for these parameters are given in terms of amplitudes having the simple structure predicted by the Amado model and it is shown how the $^{2}S$ defects will modify such predictions.