Electron-impact double ionization of He at large momentum transfer studied by second-order Born-approximation calculations

We report results of second-order Born-approximation (SBA) calculations for electron-impact double ionization of He at large momentum transfer. Comparisons are made with symmetric noncoplanar (e,3−1e) experiments at impact energies of 2080 and 4260 eV [ N. Watanabe et al. Phys. Rev. A 72 032705 (2005); Phys. Rev. A 75 052701 (2007)]. The SBA calculations clearly show that second-order two-step mechanisms play crucial roles in double ionization of He under the kinematical conditions studied. Furthermore, contributions of the two-step mechanisms are found to be more prominent with the increase in the slow ejected electron energy.