Convergent calculations of double ionization of helium: From „g ,2e... to „e ,3e... processes

The first absolute se ,3ed measurements, by Lahmam-Bennani et al. [Phys. Rev. A 59, 3548 (1999)], have been recently approximately reproduced by Berakdar [Phys. Rev. Lett. 85, 4036 (2000)] and supported by Jones and Madison [Phys. Rev. Lett. 91, 073201 (2003)], but with widely differing conclusions. The former indirectly implied that the Born-CCC-based calculations of Kheifets et al. [J. Phys. B 32, 5047 (1999)] were inaccurate due to the reliance on the first Born approximation. The latter argued that the first Born approximation was valid, but an insufficiently accurate initial state was used. We investigate these claims by performing calculations with ground states similar to those used by Jones and Madison, as well as including the second Born terms. We find the effect of the second Born terms to be negligible and that the original calculations of Kheifets et al. are reproduced if a ground state similar to that of Jones and Madison is used, but appropriately corrected as done by Le Sech and co-workers [J. Phys. B 23, L739 (1990)].