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There is no way physicists can sift through the three million events that take place every second inside the CDF detector. Nor should they really need to; most of these events will give them no new information about the particles that make up our universe. To weed out the boring events from the few that might contain evidence of new physics, or new information about the Standard Model particles, physicists at CDF have created a “trigger system” that uses software, computers, and high-speed electronics to pick out the events that are most likely to contain these rare processes.

Graphic for trigger system
Triggers are designed to identify quickly the events that are potentially interesting and discard the ones that are not. “Interesting” events usually involve the creation of rarely produced, massive particles (such as the top quark) that decay quickly, producing a spray of more common particles like electrons, muons, or tau particles. Each type of massive particle produces a distinctive spray of decay products. By designing the trigger system to record only the events that produce one of these signature decay processes, physicists increase the chances that the events they examine will teach them something new.

The trigger system has three levels, each one more selective than the one before it.

  Events/sec accepted by trigger Latency
(What is this?)
An example of the acceptance criteria of each level of trigger
Level One Trigger 10,000 to 25,000 5.5 microseconds Is there an isolated track in the silicon detector or COT?
Level Two Trigger 900 ~30 microseconds Does the isolated track correspond to a hit in the calorimeter?
Level Three Trigger 150 1 second Does the overall behavior of the particle identify it as an electron, muon, or tau particle?
  Of the three million events being produced per second, only about 150 make it through all three levels of the trigger system. It takes the trigger system a little over one second to accept an event which it deems "interesting." If the answer to all these questions is yes, the event is written to tape.


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Created by Jennifer Lauren Lee; updated January 2008 by JLL.