Higher-order contributions to ionization plus excitation cross sections in high energy e-+ He and H++ He scattering

Abstract
The authors have determined absolute cross sections for ionization-excitation of He by energetic electron and proton projectiles. Using a semi-empirical analytic formula the authors have been able to decompose their He+ (np) cross section data in leading order terms which are proportional to Zpn for n = 2, 3 and 4. In particular the authors have found a strong Zp3 dependence which appears to represent quantum interference effects. The set of amplitude coefficients obtained here is universal for both their electron and proton cross section results from He+ (np) states with principal quantum numbers n = 2 to 5.