Search for rare muon decays with the Crystal Box detector

A search with the Crystal Box detector shows no evidence for the lepton-family-number-nonconserving decays μ→eγ, μ→eγγ, or μ→eee. The search provides upper limits for the branching ratios of Γ(μ→eγ)/Γ(μ→evv¯)<4.9×${10}^{\mathrm{-}11}$ (90% C.L.), Γ(μ→eγγ)/Γ(μ→evv¯)<7.2×${10}^{\mathrm{-}11}$ (90% C.L.), and Γ(μ→eee)/Γ(μ→evv¯)<3.${510}^{\mathrm{-}11}$ (90% C.L.). In addition, a limit for the emission of a light scalar or pseudoscalar boson in radiative muon decay is given.