Search for the Lepton Flavour Violating Decay $\mu^{+} \to e^+ \gamma$ with the Full Dataset of the MEG Experiment

TL;DR

This paper reports the final results of the MEG experiment's search for the lepton flavor violating decay μ+ → e+ γ, setting the most stringent upper limit to date on its branching ratio based on the full dataset collected.

Contribution

The paper provides the most sensitive upper limit on the μ+ → e+ γ decay branching ratio using the complete dataset from the MEG experiment, improving previous constraints.

Findings

No significant excess of decay events observed.

Established an upper limit on the branching ratio of 4.2 × 10^{-13}.

Set the most stringent limit to date on this decay process.

Abstract

The final results of the search for the lepton flavour violating decay $\mu^{+} \rightarrow {\rm e^{+}} \gamma$ based on the full dataset collected by the MEG experiment at the Paul Scherrer Institut in the period 2009--2013 and totalling $7.5\times 10^{14}$ stopped muons on target are presented. No significant excess of events is observed in the dataset with respect to the expected background and a new upper limit on the branching ratio of this decay of $BR( \mu^{+} \rightarrow {\rm e^{+}} \gamma ) < 4.2 \times 10^{-13}$ (90\%\ confidence level) is established, which represents the most stringent limit on the existence of this decay to date.