The free NN interaction, 50-1000 MeV

Abstract

Phase shift solutions for pp elastic scattering are unique up to 800 MeV, and for np up to 500 MeV. There is excellent agreement between three analyses for all phase shifts δ and for elasticity parameters η of dominant inelastic partial waves (1D2, 3F3 and 3P2). For low partial waves, notably 3P0, 3P1 and 1S0, there are some disagreements about η parameters, reflecting insensitivity of elastic data and some discrepancies amongst experiments. The need for further data is reviewed. Amplitudes for np→pn between 140 and 500 MeV are known accurately from phase shift analyis, and are almost purely real; they are useful for extracting nuclear matrix elements from (p,n) reactions.The Paris potential is the best potential model fit to data up to 425 MeV, but there are some small systematic discrepancies with data. Whether or not dibaryon resonances exist at higher energies is still controversial. If they exist, they are associated with the onset of strong inelasticity, and are weakly coupled to both NN and πd chan...