  In a recent paper we showed that the collapse to a black hole in
one-parameter families of initial data for massless, minimally coupled scalar
fields in spherically symmetric semi-classical loop quantum gravity exhibited a
universal mass scaling similar to the one in classical general relativity. In
particular, no evidence of a mass gap appeared as had been suggested by
previous studies. The lack of a mass gap indicated the possible existence of a
self-similar critical solution as in general relativity. Here we provide
further evidence for its existence. Using an adaptive mesh refinement code, we
show that "echoes" arise as a result of the discrete self-similarity in
space-time. We also show the existence of "wiggles" in the mass scaling
relation, as in the classical theory. The results from the semi-classical
theory agree well with those of classical general relativity unless one takes
unrealistically large values for the polymerization parameter.
