Dynamics of Antimatter-Atom Collisions

Classical-trajectory Monte Carlo calculations have been used to study ionizing collisions between charged particles ($p,\overline{p},e^{+},e^{-}$) and He atoms at an incident velocity of 2.83 a.u. While differences in the total single-ionization cross sections for these projectiles are small, our calculations reveal large effects at all angles in the ionized electron spectra, and provide qualitative evidence for a Barkas effect in $p$ and $\overline{p}$ collisions. Experimental data agree well with our fully classical calculations, including cross sections involving ejected electrons of long wavelength.