MEG experiment

MEG (English: Mu to E Gamma ) was a particle physics experiment at the Paul Scherrer Institute that looked for the decay of a muon into a positron and a photon . This decay is extremely unlikely in the Standard Model of particle physics because the number of leptons is changed. In several new theories, particularly supersymmetry , this decay is significantly more common. MEG examined muon decays from 2008 to 2013, an improved version of the experiment to increase precision is planned.

MEG used a muon beam with 30 million muons per second that hit a plastic target . The muon rate was a compromise between a high number of investigated decays and the background of several almost simultaneous decays. The decay channel investigated generates a positron and a photon, which both fly away with an energy of 52.8 MeV but in exactly opposite directions. A scintillator made of liquid xenon with photomultipliers measured the energy of the photon, a drift chamber in a magnetic field was used to measure the energy of the positron.

In May 2016, researchers published an analysis of the entire record, the best ever limit on the decay probability : . This is a factor of 30 better than the previous upper limit of the MEGA experiment . ${\displaystyle \mathrm {B} (\mu ^{+}\to e^{+}\gamma )<4{,}2\cdot 10^{-13}}$

In 2014, plans for an improved MEG-II detector were presented. This should prove the decay, if it occurs frequently enough, or improve the upper limit of the decay probability by a further factor of 10. Data collection was supposed to start in 2016, but it was delayed.

See also

Mu3e

Web links

• MEG home page

Individual evidence

1. ^ MEG goes in search of the forbidden. June 24, 2004, accessed June 13, 2015 . 
2. ↑ MEG collaboration: Search for the Lepton Flavor Violating Decay μ + → e + γ with the Full Dataset of the MEG Experiment , arxiv : 1605.05081 (English).
3. ↑ ML Brooks et al. (MEGA Collaboration): New Limit for the Lepton-Family-Number Nonconserving Decay μ + → e + γ . In: PRL 83, 1521 . August 23, 1999. arxiv : hep-ex / 9905013 . bibcode : 1999PhRvL..83.1521B . doi : 10.1103 / PhysRevLett.83.1521 .
4. ^ MEG collaboration: Latest results of MEG and status of MEG-II . October 17, 2014, arxiv : 1410.4705v1 (English).