5 First Level Trigger Strategy

The Level-1 muon trigger concept in CMS is quite revolutionary: there are infact at a first superficial look two independent triggers.

In the first place there are fast dedicated trigger detectors used for a standard trigger design. Predefined patterns covering some (h,j) cone are associated with some pT value. A trigger is generated if at least three out of four possible hits are available for any of the programmed patterns.

On the other hand the chambers were designed in order to be self-triggering devices. The algorithm is similar to the Level-2 muon trigger in the past and present experiments: pT is assigned by means of a rough track reconstruction. A trigger is generated if at least two out of four muon stations provide compatible track segments.

While the first method is largely used and does not in principle present any particular problem to be solved, the second method works only if it is possible to tag the parent muon interaction identifying the bunch crossing in which it occured.