Mu to E Gamma

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.^[1] It is located at the Paul Scherrer Institute and began taking data September 2008.

Results[edit]

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

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

at 90% confidence level, ^[2] based on data collected in 2009–2013. This improved the MEG limit from the prior MEGA experiment^[3] by a factor of about 28.

Apparatus[edit]

MEG uses a continuous 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.

The MEG collaboration presented upgrade plans for MEG-II at the Particles and Nuclei International Conference 2014, with one order of magnitude greater sensitivity, and increased muon production, to begin data taking in 2017.^[4] More experiments are planned to explore rare muon transitions, such as Comet (experiment), Mu2e and Mu3e.

References[edit]

^ "MEG goes in search of the forbidden". CERN Courier.
^ Baldini, A. M.; et al. (MEG collaboration) (May 2016). "Search for the Lepton Flavour Violating Decay μ⁺→e⁺γ with the Full Dataset of the MEG Experiment". arXiv:1605.05081 [hep-ex].
^ Brooks, M. L.; et al. (MEGA Collaboration) (23 August 1999). "New limit for the lepton-family-number nonconserving decay μ⁺→e⁺γ". Physical Review Letters. 83 (8): 1521–1524. arXiv:hep-ex/9905013. Bibcode:1999PhRvL..83.1521B. doi:10.1103/PhysRevLett.83.1521. S2CID 119354296.
^ Renga, F (2014). "Latest results of MEG and status of MEG-II". arXiv:1410.4705 [hep-ex].

External links[edit]

MEG-II experiment record on INSPIRE-HEP

"MEG home page".

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[1] "MEG goes in search of the forbidden". CERN Courier.

[Baldini-2] Baldini, A. M.; et al. (MEG collaboration) (May 2016). "Search for the Lepton Flavour Violating Decay μ⁺→e⁺γ with the Full Dataset of the MEG Experiment". arXiv:1605.05081 [hep-ex].

[3] Brooks, M. L.; et al. (MEGA Collaboration) (23 August 1999). "New limit for the lepton-family-number nonconserving decay μ⁺→e⁺γ". Physical Review Letters. 83 (8): 1521–1524. arXiv:hep-ex/9905013. Bibcode:1999PhRvL..83.1521B. doi:10.1103/PhysRevLett.83.1521. S2CID 119354296.

[4] Renga, F (2014). "Latest results of MEG and status of MEG-II". arXiv:1410.4705 [hep-ex].

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