Electron correlation in the ionization of helium by high-energy protons and antiprotons

Following Martin and Salin we discuss how to demonstrate the presence of electron - electron dynamical correlation during the collision of a fast ion with an atom. Specifically in this paper we calculate proton - helium and antiproton - helium single- and double-ionization reference cross sections when , the electron - electron interaction, is set to zero during the collision but retained in the initial and final states. We present and critique three ways of obtaining these reference cross sections. Correlation measured in this way seems to be more important for proton projectiles than antiproton projectiles; it is especially needed at small impact parameters and for projectile energies below 350 keV.