IMPROVED FORCED IMPULSE METHOD CALCULATIONS OF SINGLE AND DOUBLE-IONIZATION OF HELIUM BY COLLISION WITH HIGH-ENERGY PROTONS AND ANTIPROTONS

Our previous forced impulse method calculations of single and double ionization of helium by protons and antiprotons have been improved by including d orbitals in the target centred basis. The calculations are in good agreement with experimental measurements of the ratio R of double to single ionization, without the 1.35 scaling factor we applied to our previous results. We also compare the separate single and double ionization cross sections to experiment and find good agreement. Experimental cross sections differential in projectile scattering angle at large angle (greater than 2.5 mrad) are compared to our impact parameter dependent ionization probabilities at small impact parameter, for the double to single ratio. The agreement is good, except at the lowest energy we have considered, 0.3 MeV.