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Double beam cut

The events of a beam particle crossing the target are distributed randomly in time, and there is a non-zero probability for more than one particle to come (and cause interactions) within a time interval shorter than our most sensitive equipment (i.e. the beam counters BC, see section 3.4.1) can resolve. This will look as a single event with abnormal properties, which we want to avoid. In the amplitude distribution of the PMT signals from the BC, one can clearly distinguish a secondary peak of the double beam events. The separation between the peaks is typically $3\times FWHM$ of the single beam peak, so that clean discrimination is possible. The beam count $B$ in formula  4.17 is corrected to represent the fraction of events after the double beam cut has been applied. The fraction of rejected events was, depending on the setting, between 2.9% and 5.4%, and known with high precision.