Angular correlation theory for double photoionization in a rare-gas atom

We consider the process of double photoionization (DPI) in a rare-gas atom as a two-step process, namely, (i) photoionization in an inner shell followed by (ii) the emission of an Auger electron from an outer shell. An angular correlation function for the two emitted electrons is defined by analogy with the theory of angular correlation in nuclear physics. An expression is obtained for this angular correlation function by a statistical method that makes use of the density and efficiency operators. The latter takes care of the attenuation of the probability of detection of an electron due to the geometrical properties of the detector. Theoretical values of the angular correlation function are obtained for DPI in xenon and these are shown to be in good agreement with the experimental results given by Kaemmerling and Schmidt [J. Phys. B 26, 1141 (1993)]