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Valid beam condition (VB) and beam counting

A gaseous Cherenkov beam counter  [29] and a geometrical veto scintillation counter provided a positive indication of a beam particle's passage through the target. This indication constituted the simplest possible form of an NA44 trigger, known as the valid beam trigger. The beam counter provided a 35 ps accurate start time reference for subsequent time of flight measurements via scintillating hodoscopes (see section  3.8.1). The beam count, provided by this detector, was needed to convert particle counts in the spectrometer into average particle yield for a given event centrality.