MEG experiment

The Mu to E Gamma (MEG) is a particle physics experiment dedicated to measuring the decay of the muon into an electron and a photon, a decay mode which is heavily suppressed in the Standard Model by lepton flavour conservation, but enhanced in supersymmetry and grand unified theories. It is located at the Paul Scherrer Institute and began taking data September 2008.

MEG use a continues muon beam (3 × 10⁷/s) incident on a plastic target. The decay is reconstructed to look for a back-to-back positron and monochromatic photon (52.8 MeV). A liquid xenon scintillator with photomultiplier tubes measure the photon energy, and a drift chamber in a magnetic field detects the positrons.

In May 2016 the MEG experiment published the world's leading upper limit on the branching ratio of this decay:

${\displaystyle \mathrm {B} (\mu ^{+}\to e^{+}\gamma )<4.2\times 10^{-13}}$

at 90% confidence level, based on data collected in 2009–2013. This improved the MEG limit from the prior MEGA experiment by a factor of about 28.

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