The make a quick assessment whether a particle shower is interesting, then store it for future analysis.
The four detector complexes have up to 10K subdetectors each, different directions and energies.
Then you propose what a certain decay sequence might look like and sift the trillion recorded explosions.
For exeample there were several dozen possible decay paths for the Higgs, but only a handful were detectable in this setup.
It took longer to analyze the data than run the machine.