The Schwinger model is the 2d QED with massless fermions. An important result about it (which I would like to understand) is that this is a gauge invariant theory which contains a free massive vector particle.
The original article by Schwinger Gauge invariance and mass, II, Phys. Review, 128, number 5 (1962), is too concise for me.
QUESTION: Is there a more detailed/modern exposition of the above result?