The detector is a sequence of techonlogies. When shooting a charged kaon beam through the first, a gas detector for PID, the first event is always an inelastic event, producing a lot of secondaries compared to other events that happen later. The same happens when using just the second detector standalone, a silicon pixel detector with this beam. The first event has an inelasitc interaction, which is rare between the Kaon and the pixel.
Could it be that some parameters related to the cross-sections in G4 are not initialised properly when the first event takes place but afterwards they get set correctly?
Hello,
you need commit some validation efforts trying to understand how well/bad Geant4 is working. Such questions are not resolved by declarations.
VI