The CMS barrel consists of 5 wheels containing 4 muon stations each. There is
one RPC plane in each muon station except MB1 and MB2, where additional planes
are installed. In the baseline design RPC cover the
range up to
.
The nominal segmentation in
of 5/16 degrees is given by the
physical size of the strips. 39 towers cover the
region between -2.4 and +2.4, giving an
segmentation of about 0.12
units, which is not constant over the whole range.
The basic logical unit (segment) of the RPC trigger covers 0.12
units in and 2.5 degrees in . It is defined by 8 strips in a
reference muon station. The logical segmentation is projective in and
[3]. In total there are 144 segments (0 -
143). Here we assign the central value of the 2.5 degree bin. RPC
-towers are assigned according to [4] from -19 to
19, corresponding to -2.4 to 2.4.
The RPC triggering is done on the basis of the hit information of 4 RPC planes.
Ideally a track will produce signals in 4 strips - the RPC detector elements
- belonging to 4 different RPC planes in the forward and/or barrel region. The
selection of these planes will mainly depend on the region concerned.
The hit strips of these 4 planes create a pattern, which will be specific for a
certain transverse momentum in a certain region. Such patterns were
calculated for different 
and values [3] and used
in the RPC hardware Pattern Comparator Trigger to assign a transverse momentum.
There is consent, that output information on the assigned value will
be restricted to 5 bits, giving 32 possible values. At the moment only 13
values are used: 7, 8, 10, 12, 14, 17, 20, 25, 30, 35, 40, 70, 100 GeV/c.
The trigger algorithm will first group hits into towers (
regions), then it will look for a sufficient number (3 or 4) of hit
planes in these towers, and may extend the search to neighbouring towers. The
hit patterns of the muon candidates are compared to predefined ones to assign a
transverse momentum. There are two algorithms available, one for low and one
for high momenta. Finally an algorithm will select the four best candidates
with an emphasis to extract the muons with highest .
A muon is considered to be triggered if at least 3 hits can be found
and its hit pattern in the RPC planes can be assigned a value.
A quality bit will discriminate between 3 or 4 hits found.