CP, T and CPT at CPLEAR

Using strangeness tagging at production time, CPLEAR measures time-dependent decay rate asymmetries between $K^0$ and $\bar{K}^0$, for picnic and semileptonic decays. Parameters describing CP, T, and CPT violation can be obtained with high precision. In the semileptonic channels neutral kaons are strangeness tagged also at the decay time, by the lepton charge, thus allowing the difference between the transition rates of $\bar{K}^0 \to K^0$ and $K^0 \to \bar{K}^0$ to be measured. In this way CPLEAR obtains the first direct measurement of T violation. By fitting the semileptonic rates under the constraint of the unitarity relation, we prove that in the reported measurement T violation is not mocked by CPT-violation effects in the decay amplitudes. Other CPLEAR measurements, only in part reported here, contribute to the experimental accuracy of the unitarity relation.