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.