Trigger systems at LHC experiments

The expected interaction rates at the LHC collider will exceed those of all previous particle physics experiments, which makes it mandatory to perform a very stringent online data selection (triggering). Event rates have to be reduced by factors of up to 107 without cutting signal events. The general-purpose experiments ATLAS and CMS pursue similar physics objectives with similar setups, while the dedicated b-physics experiment LHCb and the heavy-ion experiment ALICE have to use very specific triggering systems.