The process ${\mu }^{-}+\mathrm{nucleus}\to e^{-}+\mathrm{nucleus}$ is examined within the framework of gauge theories. We find that the rate for this reaction is much larger than what one might naively expect for a large class of models which allow the decay $\mu \to e+\gamma$. Further experimental search for this rare process is strongly urged.

• Received 1 March 1977

DOI:https://doi.org/10.1103/PhysRevLett.38.1512