The angular distribution of equal-energy electrons following double photoionization

The triply differential cross section (TDCS) for double photoionization of helium such that both electrons have the same energy is calculated for total energies of 10 eV and 20 eV above threshold. Excellent agreement with recent experimental results is obtained using a threebody Coulomb (3c) correlated final-state wavefunction. An angular distribution calculated with plane waves as the final state, multiplied by a Coulomb correlation factor arising from the normalization of the electron-electron interaction, gives good agreement with the 3C results and therefore allows the shape of the TDCS to be explained in a simple way. Some comments on a previous treatment using 'Wannier' theory are given.