New constraint on the existence of the μ+ → e+ γ decay

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Physics

Background:

• Lepton flavor violation (LFV) is a key area of investigation in particle physics.
• Standard Model of particle physics does not allow for LFV decays like mu(+) to e(+)gamma.
• New physics beyond the Standard Model may allow for such decays.

Purpose of the Study:

• To search for the lepton flavor violating decay mu(+) to e(+)gamma.
• To set a new upper limit on the branching ratio of this decay.
• To constrain new physics models by probing LFV processes.

Main Methods:

• Analysis of a combined dataset of 3.6 × 10(14) stopped muons.
• Utilized data collected by the MEG experiment at the Paul Scherrer Institut.
• Searched for characteristic signature of mu(+) to e(+)gamma decay events.

Main Results:

• No excess of events was observed above background expectations.
• A new upper limit on the branching ratio of mu(+) to e(+)gamma was set at 5.7 × 10(-13) (90% confidence level).
• This limit is four times more stringent than the previous world best limit.

Conclusions:

• The search for mu(+) to e(+)gamma decay yielded no positive signal.
• The new upper limit significantly constrains theories of new physics.
• Further experiments with increased sensitivity may be required to probe even smaller branching ratios.