The CPLEAR experiment at CERN has directly studied matter and antimatter symmetries via the measurement of the time evolution of K0 and K̄0. 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 K̄0 were tested down to the level of 10−18 GeV.
