Proton-antiproton impact-electron emission spectra of He: Comparison of theory with experiment

We study electron emission cross sections of He decaying to He⁺(1s) in the N=2 and 3 manifolds produced by fast proton and antiproton impact. Ab initio close-coupling calculations are carried out using the impact-parameter method. The electronic state during collision is expanded in terms of He wave functions obtained by the hyperspherical close-coupling method. The theory reproduces experimental findings regarding both the background and doubly excited resonances well. The resonance shapes are found to depend sensitively on the sign of the projectile charge. This is due to interference between the partial waves of the ejected electron. We analyze excitation paths that eventually lead to another interference effect between continuum and doubly excited states. We demonstrate importance of both the bound and continuum states as intermediate states. © 1996 The American Physical Society.