Electron-photon angular correlations in the electron impact excitation of argon

A coincidence technique has been used to measure angular correlations between electrons which have excited the first excited state of argon and the photons arising from the decay of this state to the ground state. The ratio of differential cross sections for the excitation of the degenerate substates and the relative phases have been deduced from the correlations for incident electron energies of 80 eV and 113 eV and electron scattering angles of 8.5 degrees . The angular correlations show poor agreement with those predicted by the Born approximation.