Neutron-proton scattering observables at 325 MeV, theε1parameter, and the tensor force

The sensitivity of neutron-proton elastic scattering observables to variations in the low angular momentum T=0 phase shifts is studied at $E_{\mathrm{lab}=325\mathrm{}}$ MeV. It is found that the J=1 coupling parameter ${\epsilon }_1$ is not well determined by existing data. This uncertainty in ${\epsilon }_1$ permits models with quite different tensor forces to describe the extant data. Implications and possible experimental resolution of such ambiguities are discussed.