Single ionization of helium by antiprotons: A case study by self-interaction-free time-dependent density-functional theory

Single ionization of helium by antiprotons in a wide energy range (5-1000 keV) has been studied by a self-interaction-free time-dependent density-functional theory. Our calculated single-ionization cross sections are in agreement with the experiments in the high-energy regime. The calculated single-ionization cross sections around the peak position are 20% lower than the recent close-coupling results as well as the experiment. In the low-energy regime, our results are lower than the close-coupling results, but still larger than the experimental one. A detailed comparison between our method and the close-coupling method is discussed. Our estimated ratios of double-to-single ionization are in agreement with the experimental measurements within a factor of 2 over the whole energy range. The limitation of the present method is discussed by comparing with the more complicated theoretical methods.