The System of Neutral K-Mesons and CP Violation

Abstract

Since 1957 we have known that the weak interaction possesses neither parity nor charge-conjugation invariance. Neither the parity operator P nor the charge-conjugation operator C are conserved.1 Until 1964, however, it was believed that the product operator CP is a conserved quantity. As a result of the CPT theorem, the time-reversal operator T would then also be conserved. From the fundamental work of Christensen et al. (1964, 1965) we know that CP symmetry is broken in the decay of the neutral K-mesons. In the course of the further experimental and theoretical investigations of the K-mesons it was shown that the CP violation is connected with a violation of time-reversal invariance, whereas there was no evidence for a violation of CPT invariance (Schubert 1970; see also Casella 1969). In Nature, past and future are thus distinguishable even on a microscopic level.