Separable potential for the neutron-proton system

A separable potential is proposed for the n-p interaction in ¹S₀ and ³S₁-³D₁ partial waves. In the singlet S state the potential fits new phenomenological phases rather accurately in the laboratory kinetic energy range 0-600 MeV; it is also capable of reproducing singlet effective-range parameters in close agreement with experiment. In the coupled state ³S₁-³D₁ the potential provides a correct description of the deuteron data (ED, pD, Q, η), while at the same time it adequately fits modern phenomenological phases up to Elab500 MeV in both the S and the D wave; triplet effective-range parameters are also in agreement with experimental data. Only the mixing parameter ε₁ deviates from predictions of phase-shift analyses. In the construction of the potential care was taken that its off-shell behavior be reasonable. As an eminent property it thus exhibits an off-shell behavior similar to the one of the Paris potential. In particular the ³S₁-³D₁ potential yields a deuteron S-state wave function, which in momentum space shows a zero like the Paris potential. Still the model is simple enough to be of good use in modern computer codes for few-body systems and other nuclear applications.NUCLEAR REACTIONS Separable potential proposed for n-p interaction; fits new on-shell data; off-shell behavior compared to Paris potential.