Double ionization of helium in fast ion collisions: the role of the correlated initial state

The momentum distribution of the electrons emitted in double ionization of helium by 100 MeV u(-1) C6+ ions has been obtained in a kinematically compl ete collision experiment. Attention is focused on the momentum components o f the electrons along the projectile axis, P-1\\ and p(2\\), which are negl igibly affected by the momentum transfer by the projectile. Calculations in the Born approximation including shake-off demonstrate that the correlated two-electron (p(1\\) , p(2\\)) final state sensitively depends on the init ial state wavefunction.