This Letter reports a new experimental search for the family-number-nonconserving decay ${\mu }^{+}\to e^{+}\gamma$. There is no evidence for the presence of this decay mode. The upper limit for the branching ratio is $\frac{\Gamma (\mu \to e\gamma )}{\Gamma (\mu \to e\nu \overline{\nu })}<4.9\mathrm{}\times {10}^{-11\mathrm{}}$ (90% confidence limit).

• Received 7 February 1986

DOI:https://doi.org/10.1103/PhysRevLett.56.2461