Information about the Two and Three Nucleon Systems Obtained and Obtainable from the Use of Polarized Targets and Beams

Review of recent experiments and theory makes it clear that the spin structure of the three-nucleon system is too complicated to allow a direct determination of the scattering matrix in the near *future. In order to provide more readily applicable tools for experimental analysis, the rigorous three-body theory provided by the Faddeev equations should be articulated to provide a low energy n-d theory comparable to effective range theory, a unitary parameterization for the coupled elastic scattering and breakup problems comparable to phase shift analysis, and a theory of high angular momentum states based on the deuteron wave function analagous to one-pion-exchange for the N-N system. As physical input we . also require both better nucleon-nucleon scattering measurements, particularly in the n-p system, and a method for extending these results to the energy-momentum regions allowed by the uncertainty principle in the threenucleon system. Whether we attempt to derive this extension from electromagnetic measurements of the two-nucleon wave functions, or directly from two-nucleon scattering, we find that this extension requires understanding of the coupling of the nucleon-nucleon system to other elementary particles. t Paper presented at the International Colloquium on Polarized Targets and Beams, C.E.N. Saclay, December 5-9, 1966,. * * Vork performed under the auspices of the U. S. Atomic Energy Commission Thanks to the high precision of recent nucleon-nucleon scattering measurements provided by polarization techniques, we find that all the characteristic features of the two-nucleon interaction can in fact be interpreted as arising from the exchange of known bosons and boson resonances, and hence that we can hope to make this extension in a physically reasonable way. We conclude that the three-nucleon problem should be approached both phenomenologically and from the point of view of elementary particle physics, and that the coupling of these two approaches offers great promise, if kept in close contact with experiment, and if full use is made of the new polarized target and polarized beam techniques. INFORMATION ABOUT THE TWO AND THREE NUCLEON SYSTEMS OBTAINED AND OBTAINABLE FROM THE USE OF POLARIZED TARGETS AND BEAMS+