New results for the neutron–deuteron analyzing power Ay(θ) at En=1.2 and 1.9 MeV and their comparison to proton–deuteron data reveal a sizeable and unexpected difference which increases with decreasing center-of-mass energy. This finding calls for the theoretical treatment of a subtle electromagnetic effect presently not incorporated in rigorous three-nucleon scattering calculations, before it is justified to invoke charge-dependent three-nucleon forces and/or other new physics.
