Intra-atomic Electron-Electron Scattering in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">p</mml:mi></mml:math>-He Collisions (Thomas Process) Investigated by Cold Target Recoil Ion Momentum Spectroscopy

Abstract

We have performed a kinematically complete experiment for the transfer ionization reaction $0.15--1.4\mathrm{MeV}p+\mathrm{He}\ensuremath{\rightarrow}{\mathrm{H}}^{0}+{\mathrm{He}}^{2+}{+e}^{\ensuremath{-}}$ by measuring the three-dimensional momentum vector of the ${\mathrm{He}}^{2+}$ ion in coincidence with the scattering angle and the plane of the ${\mathrm{H}}^{0}$. In the measured fourfold differential cross section we can clearly distinguish between the independent two-step process of capture plus ionization and the correlated $e$- $e$ Thomas scattering. We find a ${v}_{P}^{\ensuremath{-}7.4\ifmmode\pm\else\textpm\fi{}1}$ scaling for the total cross section of the $e$- $e$ Thomas process.