When LHCb is up and running, the detector will register an estimated 10 million proton collisions every second. Recording all of these ‘events’ is virtually impossible due to limited storage capacity. So, in order to cherry-pick the best of them, LHCb employs an electronic system called a ‘trigger’.
The LHCb trigger system operates on two levels. The first uses information taken in real-time from the detector – specifically from the VELO, the calorimeter, and the muon system. It selects around 1 million events per second for further processing, while discarding information from the remaining 9 million. The first level trigger works incredibly fast, making its decision in just four millionths of a second.
After filtering by the first level trigger, a very large amount of data still remains. 35 gigabytes - equivalent to 8 DVDs worth of information - is fed every second into 2,000 state-of-the-art computers, located deep underground at the LHCb site. These machines select interesting events to save for analysis, further trimming the 1 million events per second to a more manageable 2,000. This second level trigger has more time to take the decision than its first level counterpart.