We present new measurements of the analyzing power for $\mathrm{np}$ scattering at 10.03 MeV accurate to ± 1 × ${10}^{-3\mathrm{}}$. A new source of systematic error, related to resonances in $n-{}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ scattering in the neutron detectors, is discussed. The interaction of the neutron magnetic moment with the Coulomb field of the proton is found to make a significant contribution to the analyzing power at the present level of accuracy. The results are compared to predictions of nucleon-nucleon potential models. New, improved values are reported for the $p$ and $d$-wave spin-orbit phase-shift splittings.

• Received 13 June 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1561