Superscattering matrix for two-dimensional black holes.

A consistent Euclidean semiclassical calculation is given for the superscattering operator S/ in the Russo, Susskind, and Thorlacius (RST) model for states with a constant flux of energy. The S/ operator is CPT invariant. There is no loss of quantum coherence when the energy flux is less than a critical rate and complete loss when the energy flux is critical.