Radiative Decay Modes of the Muon

A 5-in. freon bubble chamber was used to search for the following decay modes of the μ⁺ meson: (1) μ⁺→e⁺+γ, (2) μ⁺→e⁺+e^-+e⁺, (3) μ⁺→e⁺+ν⁰+ν⁰+γ, (4) μ⁺→e⁺+ν⁰+ν⁰+e⁺+e^-. Two exposures were made at the Carnegie Institute of Technology synchrocyclotron. A total of 200 000 pictures were taken yielding 3.3×{}10⁵ μ⁺ meson decays.A total of 3×{}10⁵ μ⁺ decays were examined for mode (1). No decays consistent with this mode were found. The upper limit on the branching ratio Rrad was found to be ${R}rad={({{μ}}⁺{→}{e}⁺+{γ})}{({{μ}}⁺{→}{e}⁺+{{ν}}⁰+{{{ν}}}⁰)}<2.5×{}{10}^{{-}5}.A total of 3.3×{10}⁵$ ${{μ}}⁺$ decays were scanned for mode (2) and no such decays were observed. The limit on the branching ratio ${R}₃ₑ$ was found to be ${R}₃ₑ={({{μ}}⁺{→}{e}⁺+{e}^{{-}}+{e}⁺)}{({{μ}}⁺{→}{e}⁺+{{ν}}⁰+{{{ν}}}⁰)}<4×{}{10}^{{-}6}.$The internal bremsstrahlung rate (mode 3) was measured for two values of ${E}_{{γ}0}$ (the minimum photon energy detected). The results were ${R}IB={({{μ}}⁺{→}{e}⁺+{{ν}}⁰+{{{ν}}}⁰+{γ})}{({{μ}}⁺{→}{e}⁺+{{ν}}⁰+{{{ν}}}⁰)},$ ${R}IB=(1.4±{}0.4)×{}{10}^{{-}2}, {E}_{{γ}0}=10 Mev,$ ${R}IB=(3.3±{}1.3)×{}{10}^{{-}3}, {E}_{{γ}0}=20 Mev.$The rate of internal conversion of internal bremsstrahlung [mode (4)] was found to be ${R}IC={({{μ}}⁺{→}{e}⁺+{{ν}}⁰+{{{ν}}}⁰+{e}⁺+{e}^{{-}})}{({{μ}}⁺{→}{e}⁺+{{ν}}⁰+{{{ν}}}⁰)}=(2.2±{}1.5)×{}{10}^{{-}5}, {E}₀=10 Mev,$ where ${E}₀$ is the minimum energy of the internally converted ${γ}$ ray.A summary is given of previous experiments on these decay modes and results are discussed with special reference to the intermediate boson scheme of weak four-fermion interactions.