All rates in the model are treated as functions of the beam intensity. The inputs to the model are the event fractions and the gate widths. Event fractions describe how the set of all possible triggers are divided into different classes based upon the kind of physical interaction that produced them. The gate widths are the effective duration of the signals that are used to form the trigger. At first it was assumed that the tagger-OR signal would be proportional to the beam intensity, but that was observed online to be incorrect, as described below. Instead the electron beam current, as measured at the Hall B beam dump, was taken as the beam intensity measurement. Although there is some uncertainty associated with this figure, at least it is believed to be linear over the full operating range of the tagger.
The level 0 trigger is a Boolean relation between OR signals from the recoil proton detector (RPD), charged particle veto (CPV) and the tagger. The first task in calibrating the model is to fit the measured scaler rates for each of these primitive OR's.