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The first step is to acquire luminosity weighted zero-bias events. Select a trigger which (1) scales with luminosity, (2) has high enough rate so it is statistically precise, and (3) is robust against changing beam conditions. When the trigger is satisfied, wait one revolution of the LHC beams, and record the next crossing of the same bunches, whether or not any trigger is satisfied on this subsequent crossing.
When we need N simulated events for a certain time period, we select N zero-bias events recorded during this time and look up the detector conditions at those N discrete times. These conditions could be the same for some period; they could also be different for every event. We then generate and simulate signal events according to these conditions, whatever those conditions might be.
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