Tests of the Equivalence Principle with neutral kaons

We test the Principle of Equivalence for particles and antiparticles, using CPLEAR data on tagged K-0 and (K) over bar(0) decays into pi(+) pi(-). For the first time, we search for possible annual, monthly and diurnal modulations of the observables \eta(+-)\ and phi(+-), that could be correlated with variations in astrophysical potentials. Within the accuracy of CPLEAR, the measured values of \eta(+-)\ and phi(+-) 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 X 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 K-0 and (K) over bar(0) as a function of the scalar, vector and tensor interaction range. (C) 1999 Elsevier Science B.V. All rights reserved.