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Ionization of helium by relativistic highly charged ions within the symmetric eikonal approximation

We consider ionization of helium targets by impact of highly charged projectile ions in collisions at relativistic energies. The overwhelming majority of electrons emitted in such collisions have velocities in the target frame, which are much less than the speed of light. Therefore, considering the collisions in this frame we treat the electron dynamics nonrelativistically. The projectile–target coupling in the collision is described within the symmetric eikonal approximation taking explicitly into account the interaction between the projectile and all the target constituents. The relation between the symmetric eikonal and the first Born approximation is discussed in detail. Helium single ionization is considered by developing an effective three-body (projectile, ‘active’ electron, target core) model of this process in which (undistorted) initial and final states of the ‘active’ electron are described in a Hartree–Fock approximation. Using a four-body model we also briefly discuss the contribution to single ionization from simultaneous ionization–excitation. A good agreement with available experimental data has been found.