New constraint on the existence of the mu+-> e+ gamma decay

TL;DR

This paper reports a new, more stringent upper limit on the branching ratio of the lepton flavor violating decay mu+ -> e+ gamma, based on an extensive data set analyzed by the MEG experiment, with no observed excess events.

Contribution

The study provides the most restrictive upper limit to date on the mu+ -> e+ gamma decay branching ratio, improving previous limits by a factor of four.

Findings

No excess events observed over background

Upper limit on branching ratio set at 5.7 x 10^-13

Improves previous limit by a factor of four

Abstract

The analysis of a combined data set, totaling 3.6 \times 10^14 stopped muons on target, in the search for the lepton flavour violating decay mu^+ -> e^+ 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 \times 10^-13 (90% confidence level). This represents a four times more stringent limit than the previous world best limit set by MEG.