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

The hyperspherical R-matrix method with semiclassical outgoing waves introduced 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 sections obtained are in excellent agreement with experiment for the very challenging dynamical situations considered. This method is the first one to compute the final double continuum state accurately over the entire configuration space, from the vicinity of the nucleus to the asymptotic region.