在标准模型框架下，夸克味改变的中性流可以在圈图水平发生，实验上在K和B介子系统已经发现。但在夸克部分，由于强相互作用的影响使得理论预言不确定性很大，很难用来精确检验新物理信号。轻子味改变中性流过程已经在中微子震荡实验中得到证实，特别是大亚湾实验的测量进一步暗示带电轻子味(cLFV)有可能是破坏的。 在标准模型内，即使考虑到中微子的微小质量和震荡，其预言的muon轻子到电子的中性流转变率也应该很小, 实验上是不可测量的。对于cLFV过程新物理的贡献可以给出可测量的预言，相对夸克味改变中性流过程，cLFV过程没有强相互作用本底，理论可以精确预言，所以任何实验上的测量证据都会证实超出标准模型新物理的存在。COMET就是利用日本大型质子加速器设施（J-PARC）来寻找带电轻子数破坏muon-electron相干转换过程的新实验，预期灵敏度将比现有实验提高1万倍。

In the Standard Model, Flavor-changing-neutral-current (FCNC) in quark sector is predicted at loop level. The FCNC in K and B meson systems had been discovered experimentally. However, the uncertainty of the theoretical prediction is large in quark sector due to QCD dilution, it is hard to precisely test the SM and probe New Physics. In the lepton sector, the lepton-flavor-violation (LFV) was evident after the discovery of neutrino oscillation, especially, the recent measurement of theta13 from Daya Bay experiment. In the SM, even considering the tiny masses and oscillation of neutrinos, the predicted decay rate for charged-lepton-flavor-violation (cLFV), such as muon-electron conversion, is still tiny (less than 10^-54), which can not be detected in experiment. However, New Physics contributions can enhance the muon-electron conversion rate, and lead to observable signal. On the other hand, comparing to FCNC in quark sector, the cLFV can be predicted cleanly without QCD dilutions. Any experimental evidence of cLFV will indicate signal of New Physics. COMET experiment is proposed to search for the muon-electron conversion at J-PARC in Japan, and approved in 2012. According to the schedule, COMET will take first data in 2016. The sensitivity will be improved by order of 4 magnitudes (10000 times) comparing to the current experiments.