[en] Using strangeness tagging at production time, CPLEAR measures K⁰/K-bar⁰ time-dependent asymmetries in pionic and semileptonic kaon decays. From those, a set of parameters describing CP, T and CPT violation in neutral kaon mixing and decay can be determined. Strangeness tagging at decay time with the lepton charge allows for time-reversal violation to be directly observed with a significance of more than three standard deviations. The precision on each of the CPT violation parameters is discussed. The mass equality of the K⁰ and K-bar⁰ is tested within 4.x10^-19 GeV

[en] Using its unique capability of strangeness tagging at K⁰ production in pp-bar→K^±π^±K⁰(K-bar)⁰) and at decay with the lepton charge in semileptonic decays CPLEAR measured the semileptonic decay-rate asymmetry (R(K-bar)⁰→e⁺π^-ν)-R(K⁰→e^-π⁺ν-bar)/R(K-bar)⁰→e⁺π^-ν)+R(K⁰→e^-π⁺ν-bar). The asymmetry, fitted over the eigentime interval 1-20 τ_S, yielded a non-zero result of (6.6±1.3_stat±1.1_syst)x10^-3. A thorough phenomenological analysis identifies T violation in K⁰ mixing and/or CPT violation in semileptonic decays as possible interpretations. A confrontation with world data on neutral kaon decays, however, excludes the latter with sufficient precision to establish the result as the first direct observation of time reversal non-invariance

[en] A measurement of the branching ratio for K_S→e⁺e^- decay was performed with the CPLEAR detector at LEAR. Full event reconstruction together with calorimeter e/π separation allowed for powerful background rejection and high signal acceptance. The analysis on the complete set of data yields the result: BR(K_S→e⁺e^-)<1.4·10^-7 (90% CL), an improvement on the current experimental limit by a factor of 20

[en] The CPLEAR experiment at CERN has directly studied matter and antimatter symmetries via the measurement of the time evolution of K⁰ and K-bar⁰. The CPT violation parameter Re(δ) was directly measured with a precision of a few 10^-4 while Im(δ) is determined from the Bell-Steinberger relation, with a precision of 10^-5. The mass and decay-width equality between the K⁰ and K-bar⁰ were tested down to the level of 10^-18 GeV

[en] The CPLEAR experiment at CERN measured the CP and CPT violation parameters and determined in a direct way the T violation. The results allow the determination of the CPT violation parameters in the neutral kaon mixing with a precision better than a few 10^-4. The mass equality between K⁰ and K-tilde⁰ is tested down to the level of 10^-19 GeV. In addition, physics on a scale close to the Planck mass is probed for the first time

[en] We report the results of the CPLEAR experiment on CP-, T- and CPT-symmetries in the neutral kaon system. CP-violation parameters are given for different decay channels. For the first time T-violation is measured by a direct method using semileptonic decays. The CPT symmetry in the kaons decays is tested through the parameters Im(δ), from the Bell-Steinberger relation, with a precision of 10^-5 and Re(δ) with a precision of a few 10^-4 (two order of magnitude better than the previous measurement). These two measurements allow us to bound the difference in mass and width of K⁰ and K-bar⁰ to be equal within 10^-18 GeV. In the limit of CPT invariance in the neutral kaon decays, the K⁰ and K-bar⁰ masses are equal within 10^-19 GeV

[en] LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved

[en] The CPLEAR experiment uses tagged K⁰ and K⁰ produced in pp annihilation at rest to measure CP-, T- and CPT-violation parameters in the neutral kaon system. The results of these measurements and some implications are reported. (orig.)

[en] A measurement of the branching ratio for K_S→e⁺e^- decay was performed with the CPLEAR detector at LEAR. Full event reconstruction together with calorimeter e/π separation allowed for powerful background rejection and high signal acceptance. Analysis of data taken up to 1994 yields the result: Br(K_s→e⁺e^-)<4.2.10^-7(90% CL). (orig.)

[en] The CPLEAR experiment at CERN uses time-dependent decay-rate asymmetries between K⁰ and K⁰ to measure η_+-. The analysis and the systematic errors are discussed. The preliminary results from all our data are φ_+-=43.5 ±0.5 _stat±0.5_syst±0.4_Δm and vertical stroke η_+-vertical stroke =(2.316±0.025_stat±0.028_syst±0.009_τS) x 10^-3. The dominant part in the systematic error of φ_+- is due to the regeneration correction. A dedicated experiment was performed to reduce this error considerably. (orig.)