Speaker
Description
Summary
At the Large Hadron Collider (LHC), muons of large transverse
momenta are expected to play a crucial role in the physics under
study. The Compact Muon Solenoid (CMS) is a general purpose
experiment designed to study proton-proton collisions at the LHC. At
the LHC, proton beams will cross each other at a rate of 40 MHz,
producing in average 20 p-p interactions. The CMS L1 Trigger must
select interesting collisions at a rate smaller than 100 kHz. In
this report we describe the Drift Tube Track Finder (DTTF) Muon
Trigger.
CMS will combine three different technologies for precise muon
detection and efficient triggering: drift tube (DT) chambers in the
barrel region ($|\eta|<1.2$), cathode strip chambers (CSC) in the
forward region ($0.8<|\eta|<2.4$), and resistive plate chambers
(RPC) in both regions ($|\eta|<2.1$). The DT muon chambers are
located in the gaps of the barrel iron yoke. The yoke is organized
in five wheels along the detector axis. Each wheel is divided in
twelve $30^\mathrm{o}$ sectors in azimuth, and four concentric
stations in the radial direction: MB1, MB2, MB3, MB4. In every
station in a sector, one DT muon chamber contains twelve layers of
drift cells organized in two $r-\phi$ superlayers and one $r-z$
superlayer (except the MB4 chambers that do not contain $r-z$
superlayer).
The information delivered by the DT muon chambers is processed by
the DT L1 Muon Trigger, which is divided into a DT Local Trigger and
a DT Regional Trigger. Hits in the DT muon chambers are first
organized in segments and assigned a beam crossing by the DT Local
Trigger, and delivered to the DT Regional Trigger.
The DTTF system implements the DT Regional Trigger. The task of the
Drift Tube Track Finder Trigger is to reconstruct full muon tracks
originating at the interaction point, and to assign them physical
parameters.
The DTTF Trigger is physically realized using a sophisticated
electronic system. The DTTF logical segmentation replicates the CMS
barrel detector geometrical structure. The system is organized in
twelve modules stored in six crates. Each module processes the
information that originated in a $30^\mathrm{o}$ wedge of the barrel
detector. One module is formed by eight boards: six Phi Track Finder
(PHTF) sector processors (one PHTF for wheels $\pm 1$ and $\pm 2$,
and two PHTF boards for wheel 0), one Eta Track Finder (ETTF), and
one Wedge Sorter. Two modules share the same crate and the same VME
Controller, Timing, and Data Link boards. A 7th crate contains the
Trigger Timing and Control system, the Barrel Sorter, and the
interface to the CMS DAQ system.
The Phi Track Finder sector processors (PHTF) reconstruct muon
tracks in the $r-\phi$ plane. The PHTF track finding algorithm is
implemented in three logical steps: (i) Extrapolation, (ii) Track
Assembling, and (iii) Parameter Assignment (transverse momentum,
position in $\phi$, electric charge, and quality).
In every $30^\mathrm{o}$ wedge, the Eta Track Finder (ETTF)
reconstructs the muon trajectory in the $r-z$ plane. The ETTF uses a
pattern matching procedure which is implemented in three logical
steps. First, patterns of $r-z$ segments are recognized among a
predefined set ($\eta$-patterns). Second, $\eta$-patterns are
matched to PHTF tracks. Finally, if the pattern matching step was
successful, the PHTF track is assigned a fine value of $\eta$. If no
$\eta$-pattern could be matched, a rough $\eta$ value is assigned.
The DT Sorters select the four highest rank DTTF muons in the barrel
detector and, after a clean-up procedure, forward them to the Global
Muon Trigger.
The DTTF system is realized in Field Programmable Logic Array (FPGA)
technology, and is largely programmable. Its optimal exploitation
requires the setting-up of logic and lookup tables, that can even be
tuned to the physics that is to be explored. All DTTF functional
elements were specified using VHDL behavioral code. In addition,
real-time software to operate, test and monitor the system has been
produced.
The final design of the DTTF boards was decided after an extensive
prototyping phase. The PHTF and ETTF final designs concentrate
almost all the track-finding functionalities in a big Altera
Stratrix FPGA. By March 2006, all electronic boards for the DTTF
system had been produced. Quality Control of the produced boards has
almost finished.
In October 2004 the behavior of parts of the DTTF were studied under
realistic experimental conditions at the CERN Test Beam. The results
were excellent. More complex tests of the DTTF system will take
place before the LHC era. In 2006 the integrated CMS Trigger will be
tested with cosmic muons at the Magnet Test/Cosmic Challenge.
Production, installation, and commissioning of the DTTF trigger will
happen in 2006 and beginning of 2007, to be ready for the first LHC
collisions in April 2007.
