This is a measure of the total data collected at an accelerator. It is the intensity of the accelerator, summed over some specified time period. A barn^{-1 (inverse barn) of data will give one event for a process that has a cross-section of one barn. A picobarn-1 (a much larger amount of data) will give one event for a much rarer process that has a cross-section of one picobarn.}