HOWTO generate mix-in random trigger files

As described in other HOWTOs, we simulate the effect of detector noise and EM backgrounds in simulation by "mixing-in" or overlaying events collected by a non-physics trigger, usually a 100Hz "random" pulser that runs parallel but orthogonal to the main physics trigger. Generally we are using the randomtrigger_skim plugin to generate these mix-in background files. This plugin selects events collected by the random trigger described above, applies a fiducial cut on the electron beam to exclude triggers collected when the beam is off (which would not correctly represent the background), and writes the hit-level data for these events out in HDDM format.

The electron beam fiducial cut is determined by analyzing the output of the PS_flux plugin, which provides a measure of the PS coincidence rate over the run. This data and the corresponding fiducial thresholds are stored in the CCDB tables ELECTRON_BEAM/ps_counts and ELECTRON_BEAM/ps_counts_threshold. (link in Peter's documentation)

Generally the PS_flux analysis is run over skims of the PS trigger events, and the randomtrigger_skim is run over skims of the random trigger events, both of which are generated as part of the standard skimming processes. In the case that some skim files are missing or damaged, the raw data can be processed as well.

To disable the beam fiducial cut, use the command-line option RANDSKIM:USEBEAM=0.

Detailed scripts and instructions on how to run this process in detail will be provided at a later date.