Observed asymmetry in pp̄→π+K−K0/π−K+K̄0

The charge-asymmetry observed in a recent CPLEAR experiment was interpreted by the authors as a direct observation of T-noninvariance. While this is the simplest and most natural interpretation, and the observed effect agrees in sign and magnitude with theoretical expectation, adherents of T-invariance could argue that the effect observed by CPLEAR is entirely ascribable to TCP-noninvariance. This radical alternative could be excluded by sufficiently precise measurements on neutral kaon beta-decay. In any case, the CPLEAR experiment significantly restricts possible TCP-noninvariance in neutral kaon mixing.