On neutron-proton scattering

Abstract

General expressions for the nucleon-nucleon elastic scattering cross-section and polarization are derived from the transition matrix up to the orbital angular momentumL=3. A detailed investigation on the reliability of the approximation restricted to partial waves corresponding toL⩽2 has been carried out. The charge independence of nuclear forces and the continuity of the phaseshifts versus neutron energy has been taken into account. It is shown that because of the change of sign of the singletS phaseshift at about 220 MeV, following from the analysis of proton-proton data, the n-p differential cross-section at 260 MeV cannot be fitted in the lowest approximation without destroying either the continuity of the phaseshift solutions in the energy interval ranging from 27 to 260 MeV or the charge independence of nuclear forces, or both. It is also shown that the high energy n-p solutions cannot be continuously linked to the low energy ones if theS phaseshift for the singlet state is assumed positive throughout the considered energy interval. The effect of the3S1-3D1 coupling is discussed in detail at 95 MeV.