Rainbow and glory effects: Coulomb focusing and defocusing post-collision interaction in fast proton and antiproton impact

The angular dependence of the neon K-L2,3L2,3 (D-1(2)) Auger line intensity is measured and calculated for proton-neon collisions at two projectile im pact energies. At one of the energies the projectile moves faster than the Auger electron and at the other energy the projectile moves slower. The Aug er line intensity measured along the beam direction shows a significant ene rgy dependence compared with other directions. The shape and the intensity of the neon K-L2,3L2,3 (1D2) Auger line is calc ulated for proton and antiproton impact, respectively. It is used to compar e the Coulomb focusing and defocusing effect as a special case of the post- collision interaction along the beam direction. It is shown that these two types of projectile have opposite effects on Auger electrons. The analysis confirms that the post-collision interaction of a structureless heavy parti cle and light Auger electron emitted along the beam direction, as studied h ere, is a particular case of the so-called glory and rainbow effects, known from optics.