T violation and CPT tests in neutral-meson systems

The review covers transitions M0↔M¯0 in all neutral-meson systems that can show these weak-interaction transitions, M0=K0,D0,B0M0=K0,D0,B0 and BsBs. The four systems are ideal laboratories for studying the discrete symmetries T and CPT. The properties of time reversal T are discussed in classical and quantum mechanics. T violation in K0K¯0 transitions has been observed 1970 independent of assuming CPT symmetry by using the Bell–Steinberger unitarity relation. Improvements of this observation are reviewed including the latest results from 2013. They show with high significance that CP violation in K0K¯0 transitions is only T violation without any CPT violation. Transitions in the other three systems do not show CP violation so far and, therefore, neither T nor CPT violation. The large observed CP violation in B0→J/ψK0B0→J/ψK0 decays is presented to be compatible with only T and no CPT violation, the same for the significant but very small CP violation in decays K0→ππK0→ππ, I=2I=2.