Separable potential for the neutron-proton system

Abstract

A separable potential is proposed for the $n\ensuremath{-}p$ interaction in $^{1}S_{0}$ and $^{3}S_{1}\ensuremath{-}^{3}D_{1}$ 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 $^{3}S_{1}\ensuremath{-}^{3}D_{1}$ the potential provides a correct description of the deuteron data (${E}_{D}$, ${p}_{D}$, $Q$, $\ensuremath{\eta}$), while at the same time it adequately fits modern phenomenological phases up to ${E}_{\mathrm{lab}}\ensuremath{\gtrsim}500$ MeV in both the $S$ and the $D$ wave; triplet effective-range parameters are also in agreement with experimental data. Only the mixing parameter ${\ensuremath{\epsilon}}_{1}$ 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 $^{3}S_{1}\ensuremath{-}^{3}D_{1}$ 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 $n\ensuremath{-}p$ interaction; fits new on-shell data; off-shell behavior compared to Paris potential.