Abstract
The electron-photon coincidence technique has been employed in experimental investigations aimed at elucidating the finer details of the excitation of the first excited states of the heavy noble gases by electron impact since the mid 1970s. The agreement between measured data and the predictions of first-order perturbative theories such as the distorted wave Born approximation (DWBA) and the first-order many-body theory (FOMBT) ranges from good in some cases to rather poor in other cases. This article will review the current status of electron-photon coincidence experiments with the heavy noble gases, critically assess the level of agreement and disagreement between experiment and theory, discuss apparent trends in the data, make recommendations for the direction of future experiments and suggest ways to ensure that measured coherence parameters are free from instrumental and physical effects to the maximum extent possible.