Double Polarized Neutron-Proton Scattering and Meson-Exchange Nucleon-Nucleon Potential Models

Abstract

We report on polarized beam--polarized target measurements of the spin-dependent neutron-proton total cross-section differences in longitudinal and transverse geometries ( $\ensuremath{\Delta}{\ensuremath{\sigma}}_{L}$ and $\ensuremath{\Delta}{\ensuremath{\sigma}}_{T}$, respectively) between ${E}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5$ and 20 MeV. Single-parameter phase-shift analyses were performed to extract the phase-shift mixing parameter ${\ensuremath{\varepsilon}}_{1}$, which characterizes the strength of the nucleon-nucleon tensor interaction at low energies. Consistent with the trend of previous determinations at ${E}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}25$ and 50 MeV, our values for ${\ensuremath{\varepsilon}}_{1}$ imply a stronger tensor force than predicted by meson-exchange nucleon-nucleon potential models and nucleon-nucleon phase-shift analyses.