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The Implementation of the ATLAS Level-1 Muon Trigger in the Barrel Region
R.Cardarelli, F.Ceradini, A.Nisati, E.Petrolo, R.Santonico and S.Veneziano
Dipartimento di Fisica, Universita' di Roma and INFN, Roma, Italy
N. Ellis
CERN, Geneva, SWITZERLAND
June 2, 1995
Paper (Postscript)
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Abstract
The level-1 muon trigger of ATLAS in the barrel region is based on fast,
finely segmented detectors to identify penetrating charged particles, pointing
to the interaction region. The trigger is designed to unambigously identify
the interaction bunch-crossing and to provide a sharp threshold over a large
interval of transverse momentum. For the muon trigger system in the central
toroid, Resistive Plate Chambers (RPC) are proposed for their good time
resolution, easiness in the segmentation and low cost of production. The
transverse momentum selection is done with a fast coincidence between strips
of different planes. The number of trigger planes is defined by the need to
minimize the rate of accidental coincidences and to optimize the efficiency.
The different momentum selection criteria required by the physics processes
are met using a low and a high Pt triggers. In the barrel we propose to
use three trigger stations, two located close to the middle muon chambers
and one located close to the external muon chambers. The middle stations
are each made of two RPC planes and the external station is made of three
RPC planes. The low Pt trigger requires a threefold majority coincidence of
the four middle planes, while the high Pt trigger requires a twofold majority
coincidence of the three external planes and the low Pt trigger. The trigger
logic is done with a dedicated coincidence matrix circuit, based on an ASIC.
The X-Y inputs to the coincidence matrix are given by the discriminated and
shaped signals from the RPC of different planes. The transverse momentum
threshold is defined by a road in the matrix and the trigger signal is generated
when there is a valid coincidence within the road. The combination of trigger
planes and the size of the road are fully programmable. In the final design
of the trigger, three trigger threshold can be used simoultaneously in one
coincidence matrix. A coincidence matrix demonstrator ASIC was developed
and tested, within the RD27 CERN collaboration. The size of the matrix is
8x24 and the circuit can operate with two different thresholds. To implement
the low and high Pt triggers we use two ASIC's. For the low Pt trigger the
input to the ASIC are the four middle RPC planes and the logic is a 3/4
majority coincidence. For the high Pt trigger the inputs are the three external
RPC planes and the combined output of the first matrix; the logic is a (2/3
majority coincidence)x (low Pt). To compensate for different propagation
times of the signals from different detector planes, the delays of each
group of X and Y inputs to the coincidence matrix can be adjusted
inside the circuit with programmable micropipeline delays.
The demonstrator prototype of the coincidence matrix ASIC,
has been developed using a gate-array from FUJITSU in 0.5
micron CMOS technology. The trigger system is subdivided into 48
sectors and in order to minimize the cable lenght and trigger latency
the coincidence matrices will be distributed along the apparatus on boards
attached to the detector. The information from the coincidence matrices of
each sector will be collected by a local Sector Muon Trigger, located in the
center of the detector. The outputs of the sectors will be sent via optical
links to the Central Muon Trigger that generates the global muon trigger
information that is passed to the Level-1 Central Trigger Processor.
SUBMITTER'S NAME: Emilio Petrolo
SUBMITTER'S INSTITUTION: INFN Roma
ADDRESS OF INSTITUTION: Piazzale A.Moro,2 - 00185 Roma - Italy
SUBMITTER'S EMAIL ADDRESS: Petrolo@Roma1.INFN.IT
SUBMITTER'S TEL+FAX: +39-6-49914242, fax +39-6-49914320
TOPIC AREA: Level-1 muon trigger at LHC