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 PMTs 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:
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.
The MEG collaboration presented upgrade plans for MEG-II at the Particles and Nuclei International Conference 2014, with an order more sensitivity and increased muon production to begin data taking in 2017. More experiments are planned that will explore this process such as Mu2e.