Differential and Direct Differential Elastic Scattering Cross Sections for Electrons and Potassium Atoms

In a modulated crossed-beam experiment we have elastically scattered unpolarized electrons of 3.3 eV energy from spin-polarized K atoms. A measurement of the polarization of the scattered electron yields |f(θ)|²σ(θ). Our measured values of |f|²σ(θ) show a significant angular shift relative to the theoretical curve in forward-angle scattering (θ=20^∘-40^∘{}). This shift is not apparent in measurements of the differential scattering cross section σ(θ) over the same angular range, which, however, do show a significant angular shift in the range θ=50^∘-120^∘{}.