F. Leimgruber

First direct observation of time-reversal non-invariance in the neutral-kaon system

Abstract We report on the first observation of time-reversal symmetry violation through a comparison of the probabilities of K 0 transforming into K0 and K0 into K 0 as a function of the neutral-kaon eigentime t. The comparison is based on the analysis of the neutral-kaon semileptonic decays recorded in the CPLEAR experiment. There, the strangeness of the neutral kaon at time t=0 was tagged by the kaon charge in the reaction p p → K ± π ∓ K 0 ( K 0 ) at rest, whereas the strangeness of the kaon at the decay time t=τ was tagged by the lepton charge in the final state. An average decay-rate asymmetry 〈 R( K 0 t=0 → e + π − ν t=τ )−R( K 0 t=0 → e − π + ν t=τ ) R( K 0 t=0 → e + π − ν t=τ )+R( K 0 t=0 → e − π + ν t=τ ) 〉=(6.6±1.3 stat ±1.0 syst )×10 −3 was measured over the interval 1 τ S τ S , thus leading to evidence for time-reversal non-invariance.

An EPR experiment testing the non-separability of the wave function

Abstract The EPR-type strangeness correlation in the K0 K 0 system produced in the reaction p p → K 0 K 0 at rest has been tested using the CPLEAR detector. The strangeness was tagged via strong interaction with absorbers away from the creation point. The results are consistent with the QM non-separability of the wave function and exclude a spontaneous wave-function factorisation at creation (CL >99.99%).

Tests of CPT symmetry and quantum mechanics with experimental data from CPLEAR

Abstract We use fits to recent published CPLEAR data on neutral kaon decays to π + π − and πeν to constrain the CPT-violation parameters appearing in a formulation of the neutral kaon system as an open quantum-mechanical system. The obtained upper limits of the CPT-violation parameters are approaching the range suggested by certain ideas concerning quantum gravity.

Determination of the T and CPT violation parameters in the neutral kaon system using the Bell-Steinberger relation and data from CPLEAR

Abstract Data from the CPLEAR experiment, together with the most recent world averages for some of the neutral-kaon parameters, were constrained with the Bell–Steinberger (or unitarity) relation, allowing the T-violation parameter Re( ϵ ) and the CPT-violation parameter Im( δ ) of the neutral-kaon mixing matrix to be determined with an increased accuracy: Re( ϵ )=(164.9±2.5)×10 −5 , Im( δ )=(2.4±5.0)×10 −5 . Moreover, the constraint allows the CPT-violation parameter for the neutral-kaon semileptonic decays, Re( y ), to be determined for the first time. The ΔS ≠ ΔQ parameters Re( x − ) and Im( x + ) are given with an increased accuracy. The quantity Re( y + x − ), which enters the T-violation CPLEAR asymmetry previously published, is determined to be (−0.2±0.3)×10 −3 . The value obtained for Re( δ ) is in agreement with the one resulting from a previous unconstrained fit and has a slightly smaller error.

Tests of the Equivalence Principle with neutral kaons

Abstract We test the Principle of Equivalence for particles and antiparticles, using CPLEAR data on tagged K0 and K 0 decays into π+π−. For the first time, we search for possible annual, monthly and diurnal modulations of the observables |η+−| and φ+−, that could be correlated with variations in astrophysical potentials. Within the accuracy of CPLEAR, the measured values of |η+−| and φ+− are found not to be correlated with changes of the gravitational potential. We analyze data assuming effective scalar, vector and tensor interactions, and we conclude that the Principle of Equivalence between particles and antiparticles holds to a level of 6.5, 4.3 and 1.8×10−9, respectively, for scalar, vector and tensor potentials originating from the Sun with a range much greater than the distance Earth–Sun. We also study energy-dependent effects that might arise from vector or tensor interactions. Finally, we compile upper limits on the gravitational coupling difference between K0 and K 0 as a function of the scalar, vector and tensor interaction range.

Physics at CPLEAR

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 , and 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.

A determination of the CP violation parameter η+- from the decay of strangeness-tagged neutral kaons

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.

Search for CP violation in the decay of tagged K0 and K0 to π0π0π0

Abstract The CPLEAR experiment measured the eigentime-dependent asymmetry in the rates of initially tagged K 0 and K 0 decaying to π 0 π 0 π 0 in order to study the interference between the CP-violating K S and the CP-conserving K L decay amplitudes. Without assuming CPT invariance, we obtain for the CP-violation parameter η 000 the values Re( η 000 )=0.18±0.14 stat. ±0.06 syst. and Im( η 000 )=0.15±0.20 stat. ±0.03 syst. . Requiring Re( η 000 ) to be equal to Re(ϵ) we obtain Im( η 000 )=−0.05±0.12 stat. ±0.05 syst. . The corresponding upper limit for the branching ratio of the K S →π 0 π 0 π 0 decay is deduced to be B K S →π 0 π 0 π 0 −5 at the 90% confidence level.

\(\mathrm{\cal T}\)-violation and \(\mathrm{\cal CPT}\)-invariance measurements in the CPLEAR experiment: a detailed description of the analysis of neutral-kaon decays to \(\mathrme \pi \nu\)

Abstract. A detailed description of the analysis of neutral kaons decaying to

Evaluation of the phase of the CP violation parameter η+− and the KL - KS mass difference from a correlation analysis of different experiments

\mathrme \pi \nu