Ionization of helium by proton and anti-proton impact: a finite-element discrete-variable approach

We have modified our finite-element discrete-variable approach [1] to describe the response of a helium atom to an intense short laser pulse to allow for the treatment of a charged projectile. This requires the replacement of the electric dipole operator by the Coulomb interaction between the target and the projectile, which we assume to move along a straight line with a fixed impact parameter. The initial state is propagated in time using an efficient Arnoldi-Lanczos scheme. Calculations for single and double ionization of He by proton and anti-proton impact yield good agreement with experiment~[2-4] and theoretical predictions from other sophisticated non-perturbative approaches~[5,6]. In addition to angle-integrated observables, angle-differential cross sections as well as linear-momentum and energy distributions for double ionization will be presented. [1] Xiaoxu~Guan, K. Bartschat, and B.I.~Schneider, Phys. Rev. A~{\bf 77} (2008), 043421. [2] L.~H. Andersen {\it et al.}, Phys. Rev. A~{\bf 41} (1990), 6536. [3] P.~Hvelplund {\it et al.}, J. Phys. B~{\bf 27} (1990), 925. [4] H.~Knudsen {\it et al.}, Phys. Rev. Lett.~{\bf 101} (2008), 043201. [5] M.~Foster {\it et al.}, Phys. Rev. Lett.~{\bf 100} (2008), 033201. [6] M.~Foster {\it et al.}, J. Phys. B~{\bf 41} (2008), 111002.