PROTON-ANTIPROTON IMPACT ELECTRON-EMISSION SPECTRA OF HE - COMPARISONOF 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 impa ct-parameter method. The electronic state during collision is expanded in terms of He wave functions obtained by the hyperspherical close-co upling method. The theory reproduces experimental findings regarding b oth the background and doubly excited resonances well. The resonance s hapes are found to depend sensitively on the sign of the projectile ch arge. This is due to interference between the partial waves of the eje cted electron. We analyze excitation paths that eventually lead to ano ther interference effect between continuum and doubly excited states. We demonstrate importance of both the bound and continuum states as in termediate states.