T violation and CPT tests at CPLEAR

The CPLEAR experiment at LEAR/CERN employed the high flux of antiprotons stopped in hydrogen to produce, via strong pp interaction, neutral kaons strangeness-tagged at the production time t=0 by the charge of the associated charged kaon. At the decay time t=τ, in the semileptonic decay, the strangeness of the neutral kaon is tagged by the lepton charge. In this way, the probabilities of a K0 transforming into a K0 and vice versa as a function of the neutral-kaon proper time can be determined, yielding a direct measurement of T violation. Other semileptonic decay asymmetries allow to set lower limits on CPT violating parameters. Together with the Bell-Steinberger unitarity relation, it can be shown that the directly measured violation of T invariance in the mixing cannot be mimicked by CPT violation. Finally, very low limits are established for possible K0−K0 mass and decay-width differences.