Absolute differential cross sections for photo double ionization of heliumfrom the ab initio hyperspherical R-matrix method with semiclassical outgoing waves

The hyperspherical R-matrix method with semiclassical outgoing waves introd uced by us previously [Phys. Rev. A 60, 3667 (1999)] is applied to the one- photon double ionization of the He atom. The absolute differential cross se ctions obtained are in excellent agreement with experiment for the very cha llenging dynamical situations considered. This method is the first one to c ompute the final double continuum state accurately over the entire configur ation space, from the vicinity of the nucleus to the asymptotic region.