Comment on Neutron-Proton Spin-Correlation Parameter A_{ZZ} at 68 Mev

Abstract

We present two arguments indicating that the large value for the ${ϵ}_1$ mixing parameter at 50 MeV, which the Basel group extracted from their recent $A_{zz}$ measurement, may be incorrect. First, there are nucleon-nucleon (NN) potentials which predict the ${ϵ}_1$ at 50 MeV substantially below the Basel value and reproduce the Basel $A_{zz}$ data accurately. Second, the large value for ${ϵ}_1$ at 50 MeV proposed by the Basel group can only be explained by a model for the NN interaction which is very unrealistic (no $\rho$-meson and essentially a point-like $\pi NN$ vertex) and overpredicts the ${ϵ}_1$ in the energy range where it is well determined (150--500 MeV) by a factor of two.

Comments: 6 pages text (LaTex) and 2 figures (paper, will be faxed upon request), UI-NTH-9303