Search for the Decayμ+→e++γ

Abstract

A search has been conducted for the decay ${\mu }^{+}\to e^{+}+\gamma$ using spark chambers, scintillators, and fast oscilloscopes. The number of stopped pions, 7.39×${10}^9$, and the detection efficiency of the apparatus for $\mu \to e+\gamma$ events, 3.9%, would predict the detection of 3 events for a branching ratio of ${10}^{-8\mathrm{}}$. No evidence for the existence of this decay was found. The distribution in range of the $e^{+}$ in graphite, and of the ($e,\gamma$) angle for the events found near 180° was consistent with that expected from ${\mu }^{+}\to e^{+}+\nu +\overline{\nu }+\gamma$. The probability of finding the observed distribution was calculated to be greatest for an assumed $\mu \to e+\gamma$ branching ratio of zero. This probability drops below 50% of this value if the branching ratio is 0.6×${10}^{-8\mathrm{}}$, and below 10% for 2.2×${10}^{-8\mathrm{}}$.