CP violation in rare K decays

In this thesis selected rare decays of the K0 meson were analyzed in the framework of the standard model. The interest layed in first line in decays, in which CP violation can play a great role and aim was, to show possible CP violating observables. For this the relevant different decay mechanisms were identified under inclusion of latest experimental data and their interaction, which leads to partly large interference effects, studied. In chapter 2 the decays KL→π0l+l- were analyzed, the amplitudes of which consist of comparable contributions of CP conserving and CP violating mechanisms. The base for the discussion of the CP conserving amplitude formed an analysis of the decay KL→π0γγ. The calculation of a directly CP violating component on the base of an effective Hamiltonian for the transition s→dl+l- yielded a branching ratio for typical values of the top mass and the CP violating phase of the CKM matrix of similar 1.5.10-12. In chapter 3 the decay KL→π+π-e+e- was the main topic. The consideration of this decay as conversion process of the radiative decay KL→π+π-γ allows the measurement of a CP violating circular polarization of the photon via the correlation between the e+e- and the π+π- plane. A CP violating asymmetry of 14%. In the complete angular distribution of the final state of KL→π+π-e+e- two further CP violating observables were identified. On of these observables is dependent on the presence of an axial-vector electron current in the matrix element and is therefore a measure of the direct CP violation. In chapter 4 the decays KL,S→π0π0e+e- were analyzed. A support of this analysis formed first the study of the quadrupole transitions KL,S→π0π0γ with an estimation of the branching ratio of similar 1.10-8 respectively similar 2.10-11. Combinations of the real and virtual photon contributions yielded the amplitude for the transition KL→π0π0e+e-