Comment on "Phase-Shift Analysis of NN Scattering Below 160 Mev: Indication of a Strong Tensor Force"

Abstract

In his recent publication of a NN phase shift analysis below 160 MeV, Henneck reports relatively large values for the mixing parameter $\epsilon_1$. Based on these results, Henneck suggests that the strength of the $\rho$-meson tensor coupling to the nucleon may be weaker than used in present day NN interactions, like the Paris or Bonn potentials. We point out that at low energies ( < 100 MeV ) there is very little sensitivity to the strength of the $\rho$ coupling, due to the compensating effect of the second order tensor term. In order to establish sensitivity, one has to go to energies > 200 MeV, where the second order contribution has gone out. As it happens, the $\epsilon_1$ mixing parameter is well determined in the region of energies 200--300 MeV, and there is agreement with the predictions by the Paris and Bonn potentials; whereas the weak-$\rho$ model is about 50\% above the data. This and additional considerations in triplet $P$-waves re-confirm that NN scattering requires the strong $\rho$, consistent with the $\pi\pi-N\bar{N}$ partial-wave analysis by H\"ohler and Pietarinen.