The µ→eγ decay represents one of the most sensitive probes towards new physics. It is in fact forbidden within the Standard Model, but new scenarios such as supersymmetry and grand-unified theories predict branching ratios for this process that could be just around the corner. A positive evidence would be an unambiguous signature of new physics, while improvements on the existing limit would constrain the parameter space of many models. The MEG experiment at the Paul Scherrer Institut (Villigen, CH) is searching for this decay using a magnetic spectrometer coupled to an innovative liquid xenon scintillation detector. Constant calibrations and monitoring are performed with, among other things, multi-MeV γ-rays from nuclear reactions by both protons from a dedicated Cockcroft-Walton accelerator and neutrons from a pulsed DD generator.
The latest MEG results coming from the combined analysis of 2009 and 2010 data set a 90% confidence level limit on the decay to 2.4x10–11 . This supersedes the previous limit set by the MEGA experiment by a factor of 5.
