Neutron-proton spin-correlation parameterAzzat 68 MeV

We report a first measurement of the spin-correlation parameter ${\mathit{A}}_{\mathit{z}\mathit{z}}$ in neutron-proton scattering at 67.5 MeV. The results, obtained in the angular range 105°≤${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$≤170° with typical accuracies of 0.008, are highly sensitive to the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$ ${\mathrm{-}}^3$ ${\mathit{D}}_1$ mixing parameter ${\mathrm{\epsilon }}_1$. A phase-shift analysis based on the current world data yields a value of ${\mathrm{\epsilon }}_1$ significantly higher than predicted by modern potential models.