# About muons, taus and the number of generations

there! Why cannot consider the muon or the tau just like excited states of the electron (and similarly, with the (u,d) (c,s) (t,b) pairs? I guess that it is related to the absence of decays like

muon-> electron+photon

and similar stuff. But, is there any other reason?

• My understand is that $\mu \rightarrow e + \gamma$ is forbidden in the standard model. – John Rennie Feb 24 '14 at 19:55