New Constraint on the Existence of the μ + → e + γ Decay

The analysis of a combined data set, totaling $3.6\ifmmode\times\else\texttimes\fi{}{10}^{14}$ stopped muons on target, in the search for the lepton flavor violating decay ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$ is presented. The data collected by the MEG experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and yield a new upper limit on the branching ratio of this decay of $5.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ (90% confidence level). This represents a four times more stringent limit than the previous world best limit set by MEG.

• UD
  U.S. Department of Energy