An experimental test of charge symmetry in N‐P elastic scattering

An experiment is described to investigate the isospin‐mixing, charge‐symmetry breaking component in the n‐p interaction. The experiment measures the difference ΔA between the neutron and proton analyzing powers An and Ap in n−p elastic scattering at 500 MeV. The experiment consists of two interleaved phases in which polarised neutrons, respectively unpolarized neutrons are scattered from an unpolarized, respectively polarized proton target of the frozen spin type. Designed as a null measurement requiring no accurately known polarization standards, the experiment determines the difference in angle at which An and Ap cross through zero. It is intended to provide an unambiguous test of class IV charge‐symmetry breaking effects to the level of ΔA≂0.001, corresponding to a laboratory angle difference at zero crossing of ∼0.05°.