The decay products of the K0 are the tracks in red (3 and 4). A charged pion (Track 1) and a charged Kaon (Track 2) are created in association with the K0 in the pp= annihilation.
The charge of the Kaon defines the flavour of the neutral Kaon at the time of the production. The charged tracks are reconstructed with two proportional chambers and six driftchambers. Particle identification is provided by a threshold Cerenkov counter sandwiched between two scintillators.