Sep 25 – 29, 2006
Valencia, Spain
Europe/Zurich timezone

The Level-0 muon trigger for the LHCb experiment

Sep 26, 2006, 2:40 PM
Valencia, Spain

Valencia, Spain

IFIC – Instituto de Fisica Corpuscular Edificio Institutos de Investgación Apartado de Correos 22085 E-46071 València SPAIN


Jean-Pierre Cachemiche (CPPM IN2P3/CNRS)


The Level-0 muon trigger looks for straight tracks crossing the five muon stations of the muon detector and measures their transverse momentum. The tracking uses a road algorithm relying on the projectivity of the muon detector. The Level-0 muon trigger analyzes every LHC bunch crossing. It handles about 130 GBytes per second. It finds muon tracks for a bunch crossing in about one microsecond. The architecture is pipeline and massively parallel. The processor is based on high speed optical and copper links, custom backplane as well as on the Stratix GX family of FPGA.


The Level-0 trigger is an important part of the LHCb trigger reducing the bunch
crossing rate from 40 MHz down to 1 MHz in less than four microseconds. It is
composed of three sub-triggers: the Level-0 calorimeters trigger, the Level-0 muon
trigger and the pileup system.

The muon detector is composed of five tracking stations equipped with 1368
Multi-Wire-Proportional-Chambers and 24 triple-GEM chambers. Each station is divided
into four regions, with increasing distance from the beam axis. The chamber topology
is complex depending on the station and on the region occupied. In addition,
chambers are equipped with pads or strips. The layout of the channel is projective
to ease the Level-0 muon trigger processing. The latter receives 25,920 bits every
25 nanoseconds.

The muon detector is divided in four quadrants. Each quadrant is connected to a
Level-0 muon processor. These four processors are identical. They are composed of
twelve processing boards, a controller board and a custom backplane. A processing
board houses four processing elements, a best candidates selection unit and a credit
card PC. A processing element analyzes the data coming from a “muon tower”
corresponding to 1/48 of a quadrant. It is connected to the five muon stations
through eight high speed optical links running at 1.6 Gbps. A processing element is
embedded in an FPGA from the Stratix GX family. Processing elements have to exchange
a huge number of logical channels to avoid inefficiency on the border of a tower.
Copper serial links running at 1.6 Gbps are used between processing elements and on
a custom backplane.

All boards are in production now. A processing board, the key element of a
processor, is a 9U board with a width of 220 mm. It contains five Stratix GX, about
1500 components and seven pressfit connectors. The printed circuit is made of 18
layers. The minimal size of the track and the minimal distance between two tracks is
120 microns. The total number of links running at 1.6 Gbps is close to 100. The
impedance of these tracks is controlled within 10%. High speed serializers and
de-seriliazers are those embedded in FPGAs.

Dedicated software tools have been developed to handle the complexity of the data
flow. Dedicated tests have been prepared to validate boards during production and to
validate a processor in our institute before its installation at CERN.

Primary authors

Andreï Tsaregorodtsev (CPPM IN2P3/CNRS) Elie Aslanides (CPPM IN2P3/CNRS) Frédéric Marin (CPPM IN2P3/CNRS) Jean-Pierre Cachemiche (CPPM IN2P3/CNRS) Julien Cogan (CPPM IN2P3/CNRS) Olivier Leroy (CPPM IN2P3/CNRS) Pierre-Louis Liotard (CPPM IN2P3/CNRS) Pierre-Yves Duval (CPPM IN2P3/CNRS) Renaud Le Gac (CPPM IN2P3/CNRS) Stéphane Favard (CPPM IN2P3/CNRS)

Presentation materials