1. Rescigno T. N., Baertschy M., Isaacs W. A., McCurdy C. W., Science286(2474), (1999).
2. Rösel T., et al., J. Phys.824, 3059 (1991).
3. Röder J., et al., Phys. Rev. A53, 225 (1996).
4. Whelan C. T., et al., Phys. Rev. A50, 4394 (1994).
5. An (e 2e) experiment measures the triple differential cross section that is the number of events corresponding to two final state electrons detected at fixed position in space with well-defined energies per unit time per unit scatterer as compared with the incident flux.