A new upper limit for the decay μ+ → e+γ

Abstract A search for the decay μ + → e + γ , performed at SIN, yields a nwe upper limit R μ → eγ −9 (90% confidence). Electrons and photons from the decay of 7.5 × 10 11 stopped μ + were measured with two NaI(T1) detectors at 180° (1.2% efficiency for μ + → e + γ ). Their distribution in the region E e , E γ > 26 MeV shows agreement with the theory for μ + → e + ν ν γ .