Energy dependence of the ($e,2e$) recoil/binary peak ratio across He autoionizing levels

In previous work we reported out-of-plane $(e,2e)$ measurements and calculations for helium auto\-ionizing levels. The results were presented as $(e,2e)$ angular distributions\footnote{B.A. deHarak, K. Bartschat, and N.L.S. Martin, Phys. Rev. Lett. {\bf 100}, 063201 (2008)} and $(e,2e)$ energy spectra\footnote{B. A. deHarak, K. Bartschat, and N. L. S. Martin, Phys. Rev. A {\bf 82}, (2010) 06270} of ejected electrons. The angular distributions, which were energy integrated across an energy window of 0.3~eV for each resonance, showed a pronounced recoil peak for both $(2p^2)^1\negthinspace D$ and $(2s2p)^1\negthinspace P$, whereas that for direct ionization was negligible. We are currently measuring the energy dependence (in 30meV steps) of the recoil/binary peak ratio across these two resonances; theory predicts a rapid variation of this ratio. We will present our results and compare them with first and second order theoretical calculations.