Neutron–proton analyzing power at 12 MeV and inconsistencies in parametrizations of nucleon–nucleon data

Abstract We present the most accurate and complete data set for the analyzing power A y ( θ ) in neutron–proton scattering. The experimental data were corrected for the effects of multiple scattering, both in the center detector and in the neutron detectors. The final data at E n = 12.0 MeV deviate considerably from the predictions of nucleon–nucleon phase-shift analyses and potential models. The impact of the new data on the value of the charged pion–nucleon coupling constant is discussed in a model study.