Its underpinnings came in an experiment by Chieng-Shiung Wu involving cobalt-60, and studies of this in kaon decay won a Nobel prize for James Cronin and Val Fitch.  
This phenomenon in leptons may be observed using the Mikheyev-Smirnov-Wolfenstein effect. The NA48 experiment at CERN is currently studying this phenomenon in hyperons, and the BaBar experiment at SLAC and the Belle experiment at KEK have determined it to be true for b-mesons. Its underpinnings came in an experiment by Chieng-Shiung Wu involving cobalt-60, and studies of this in kaon decay won a Nobel prize for James Cronin and Val Fitch.  A possible explanation of the dominance of matter over antimatter, FTP, name this phenomenon, present under the weak force, in which symmetry between particles and antiparticles, as well as between a system and its mirror, are infringed.
This phenomenon in leptons may be observed using the Mikheyev-Smirnov-Wolfenstein effect.
CP-violation or charge-parity violation