Student Excellence Award Finalist: Ejected Electron-Energy and Angular Dependence of Fully Differential Ionization Cross Sections in Proton Collisions with He and H$_{\mathrm{2}}$

We have measured fully momentum-analyzed recoil ions and scattered projectiles, produced in ionizing collisions between protons and He and H$_{\mathrm{2}}$, in coincidence. The momentum of the ejected electron was then deduced from momentum conservation. From the data we extracted fully differential ionization cross sections (FDCS) for a large number of ejected electron energies ranging from well below to well above the projectile -- electron velocity matching regime. Furthermore, for each electron energy data were obtained for four different projectile scattering angles. Various signatures of the post-collision interaction were identified in the electron energy- and angular dependence of the FDCS and systematically analyzed. The data were compared to two different, but conceptually very similar distorted wave calculations. This comparison demonstrates the limitations of perturbative models under conditions where the post-collision interaction is strong and thus the need for non-perturbative methods in order to advance our understanding of the underlying few-body dynamics. Furthermore, our results show that the post-collision interaction is surprisingly strong even for electrons not ejected in the forward direction.