Double ionization of helium by electron impact: angular distributions at low incident energy

A complete analysis of our recent (e, 3e) experiments on helium at 601 eV incident energy (Lahmam-Bennani et al 2003 Phys. Rev. A 67 010701) is conducted by using an approximate 6C model which accounts for the interaction between all four particles (the scattered electron, the two ejected electrons and the nucleus) in the final state. An accurate wavefunction for the initial state is also used. The agreement between experiments and theory is not always good even though most peaks and dips can be explained. Comparison is also made with the results of the first Born-BBK approximation as well as with approximate second Born results.