Critical phenomena of collapsing massless scalar wave packets
  An analytical model that represents the collapse of a massless scalar wave packet with continuous self-similarity is constructed, and critical phenomena are found. In the supercritical case, the mass of black holes is finite and has the form $M \propto (p - p^{*})^{\gamma}$, with $\gamma = 1/2$. 
Anzhong Wang and Henrique P. de Oliveira