Deadtime in Triggers: Explained

[kelly0303]

Hello! This is probably a silly question, but I am still confused about it and I really don't have any experience with experimental physics. So I understand that a trigger system has a deadtime, which is defined as the time after which the trigger makes its choice, in which no new events can be recorded. Just to make sure I understand, does this mean that (say) you have a particle hitting your detector and during the time it takes for the trigger to decide whether to keep this event or not (deadtime), any other particle hitting your detector will be ignored? And is the deadtime the same, whether you keep that event or not? Also, are these particles hitting the detector during deadtime just discarded, usually, or are they put it a queue and passed to the trigger at a point? Thank you!

 

[mfb]

It doesn't have to be the time the trigger needs to decide. For a very simple trigger system that might be the case, but if you expect high event rates you typically implement something better - buffers that can store more data until a trigger decision has been made, for example. Then you only get dead time if this buffer gets full (too many events within a short time?).
More complex detectors will often have multiple trigger systems that work together.

 

[kelly0303]

It doesn't have to be the time the trigger needs to decide. For a very simple trigger system that might be the case, but if you expect high event rates you typically implement something better - buffers that can store more data until a trigger decision has been made, for example. Then you only get dead time if this buffer gets full (too many events within a short time?).
More complex detectors will often have multiple trigger systems that work together.

Thank you! So this means that you can save some of the data, even if it doesn't get processed on the spot. However, if the buffer is full, the data received in that period is completely ignored, right?

 

[mfb]

If you run out of space to store data you have to throw away something. What is done depends on the detector you are looking at.

 

[Tom.G]

A somewhat different source of deadtime is found in Geiger-Mueller detectors. These operate by detecting when a particle initiates an electrical avalanche breakdown of the contained gas. If a second particle arrives while the first avalanche is occurring, there is no way to discern that second particle. IIRC, the same situation occurs in at least some solid state detectors. The solution, of course, is to have an array of detectors and their support electronics rather than a single large detector.