The (e,2e) recoil peak to binary peak ratio as a function of the ejected-electron energy is reported for helium autoionizing levels (2p2)1D and (2s2p)1P. A special out-of-plane geometry is used where the ejected electrons are detected in a plane that includes the momentum transfer axis but is perpendicular to the scattering plane. The measured recoil peak to binary peak ratio is a dimensionless quantity that can be directly compared with calculations. A second-order model in the projectile-target interaction correctly reproduces the observed energy dependence and magnitude of the ratio, while a first-order model does not.

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Published in Physical Review A: Atomic, Molecular, and Optical Physics, v. 89, article 012702, p. 1-4.

©2014 American Physical Society

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