Measurement of exchange and spin-orbit effects and their interference in elastic e-Cs scattering at 7 eV

Twenty years ago a theoretical analysis showed that electron scattering by high-Z one-electron atoms might lead to interference of exchange and spin-orbit interactions at low electron energies, observable as a cross-section asymmetry if unpolarized electrons are scattered by polarized cesium atoms. By using a highly polarized cesium atomic beam, we studied exchange and spin-orbit effects at different electron energies, starting at 20 eV and going down. We observed the first distinctly non-zero interference asymmetry at 7 eV: Over the angular range of 35 to 145°, it varies between +0.02 and ?0.02 and goes through zero near 110° being negative at larger angles.