Triggering at LHC experiments

Triggering and Data Acquisition is one of the extraordinary challenges facing experiment designers at the high luminosity LHC collider. For the nominal LHC design luminosity of 1034 cm−2 s−1, an average of 17 events occurs at the beam crossing frequency of 25 ns. This input rate of 109 interactions every second must be reduced by a factor of at least 107 to about 100 Hz. Custom hardware processors make an initial decision to keep an event in a few μs using coarsely segmented data from a subset of the detectors, while holding all the high-resolution data in pipelined memories. Commodity processors make subsequent decisions using more detailed information from all of the detectors in more sophisticated algorithms that eventually approach the final reconstruction.