Muon rare decay mode search

We intend to study the grand unification theory of paritlce physics by searching for muon rare decays forbidden in the framwork of the standar model at facilities where intense muon beam is available.

MEG appratus

Purpose and Vision

It is predicted in the models beyond the starndard model that there can be muon decays in which lepton-flavor conservation is violated.

In this group searches for (1) muon decaying to an electron and a gamma ( μ->eγ decay ) and (2) muon converting to electron in muonic atoms (μ-e conversion) are being conducted with the world's highest sensitivity to determine the branching ratios. These experimental results will provide us indispensable information to understand the behavior of elementary particles at very high energy.

For the purpose of the muon rare decay search, the high intensity muon beam is necessary. For the μ->eγ search experiment we are conduging the MEG experiment using a intense DC muon beam provided at Paul Scherrer Insitute (PSI) in Switzerland. Thirty milions of muons can be provided every secaond at PSI. We have completed physics data taking which started in 2009 to reach the experiment sensitivity of one over 10 trillion (10-13). The μ-e conversion seach, on the other hand, needs a pulsed muon beam to improve the physics sensitivity over the previous bound. We are leading an international collaboration (COMET collabartion) to do this search. The μ-e conversion process has only one electron with a characteristic energy at its final state. The pulsed beam structure is required to select this signal electron from background events. Therefore extremely clean plused beam plays a key role in the experiment. We are promoting R&D work, design and construction of the experimnet with collaboration members from many countries in the world to achieve the physics sensisitivty of 1 over ten quadrillion (1016).

COMET experiments


muon: 2nd generation lepton with chage in three generations. Electron is a lepton belonging to 1st generation. In the 3rd generation there is a taw lepton. There are corresponding neutrinos in each generation.

flavour mixing: In the framwork of the starndard model, the lepton number (flavor) is convserved in any reaction. In the normal muon decay (μ->eν(anit)ν) the flavor is conserved owing to a neutrino and an anti-neutroino in the final start.

Flavor mixing means a phenomenum such as violating this conservation law.


MEG experiments 
DeeMe experiments 

Related research group

MEG Japanese group 
J-PARC Hadron beam line group
Cruogenics group 
Electronics System group 
g-2 R&D group 

Related facilities

J-PARC Hadron Experimental Facility