This chapter shows how Ke4 events are selected and background is rejected. After the definition of cuts it is also shown how the remaining background is subtracted.
In order to select Ke4 candidates, a code in C was written as part of the NA48 analysis program COmPACT. In this code, each event is tried to be reconstructed as Ke4. Only clean events are accepted, ambiguous or incomplete events are rejected.
The algorithm in detail is: