Calculated cross sections for the double excitation of helium by charged particle impact

After the recent work of Moretto-Capelle et al (1997 Phys. Rev. Lett. 76 5230) the direct comparison of the theoretical double-excitation cross sections with experiment became possible. Cross sections for the excitation of the (2s(2))S-1, (2s2p)P-1 and (2p(2))D-1 states of helium are calculated for proton and antiproton projectiles over a wide impact energy range. Our results are in good agreement with the experimental data. The dependence of the cross sections on the sign of the projectile charge, the importance of the different mechanisms causing the two-electron transitions and the obtained magnetic sublevel populations are also analysed.