CPLEAR results on T and CPT violation

We report the results of the CPLEAR experiment on T and CPT symmetries in the neutral-kaon system. Time-reversal non-invariance is observed for the first time by comparing the probabilities of a K̄0 transforming into K0 and of K0 transforming into K̄0 as a function of the neutral-kaon eigentime. CPT invariance is tested by measuring the parameter Re(δCPT) with a precision of a few 10−4, while Im(δCPT) is determined from the Bell–Steinberger relation, with a precision of 10−5. Moreover, the Bell–Steinberger constraint allows the CPT violation parameter Re(y) for the neutral-kaon semileptonic decays to be determined for the first time.