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Copyright © 2000 OPNET Technologies, Inc.
Title – 1
Distributed Trigger System for the LHC experiments
Krzysztof Korcyl
ATLAS experiment laboratory
H. Niewodniczanski Institute of Nuclear Physics, Cracow
Copyright © 2000 OPNET Technologies, Inc.
Title – 2Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Contents
• LHC
• physics program
• detectors (ATLAS, LHCb)
• LHC T/DAQ system challenges
• T/DAQ system overview
• ATLAS
• LHCb
•T/DAQ trigger and data collection scheme
• ATLAS
• LHCb
Copyright © 2000 OPNET Technologies, Inc.
Title – 3Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
CERN and the Large Hadron Collider, LHC
LHC is being constructed underground inside a 27 km tunnel. Head on collisions of very high energy protons. ALICE, ATLAS, CMS, LHCb - approved experiments.
Copyright © 2000 OPNET Technologies, Inc.
Title – 4Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
The ATLAS LHC Experiment
Copyright © 2000 OPNET Technologies, Inc.
Title – 5Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
The LHCb LHC Experiment
Copyright © 2000 OPNET Technologies, Inc.
Title – 6Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
The LHCb LHC Experiment - an event signature
Copyright © 2000 OPNET Technologies, Inc.
Title – 7Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Challenges for Trigger/DAQ system
The challenges:
• unprecedented LHC rate of 109 interactions per second
• large and complex detectors with O (108) channels to be read out
• bunch crossing rate 40 MHz requires a decision every 25 ns
• event storage rate limited to O (100) MB/s
The big challenge: to select rare physics signatures with high efficiency while rejecting common (background) events.
• E.q. H yy (mH 100 GeV) rate is ~ 10-13 of LHC interaction rate
Approach: three level trigger system
Copyright © 2000 OPNET Technologies, Inc.
Title – 8Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
ATLAS Trigger/DAQ - system overview
CALO MUON TRACKING
LVL1Pipeline
memories
Regions of
Interest
LVL2
Event builder
Data Recording
Readout Driver
Readout Driver
Readout Driver
Readout Buffer
Readout Buffer
Readout Buffer
Interaction rate ~ 1 GHz
Bunch crossing rate: 40 MHz
rate : 100 kHz
latency: < 2.5 s
throughput 200 GB/s
rate : 1 kHz
latency: <10ms>
throughput 4 GB/s
rate : 100 Hz
latency: <1 s>
throughput 200 MB/s
• LVL1 decision based on course granularity calorimeter data and muon trigger stations
• LVL2 can get data at full granularity and can combine information from all detectors. Emphasis on fast rejection. Region of Interest (RoI) from LVL1 are used to reduce data requested (few % of whole event) in most cases
• EF refines the selection according to the LVL2 classification, performing a fuller reconstruction. More detailed alignment and calibration data can be used
EF
Copyright © 2000 OPNET Technologies, Inc.
Title – 9Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
EF SUBFARM
ROS
ROD
ROS ROS ROS ROS
DFML2SVRolB
LVL2 FARMEF SUBFARM
SFI
L2PU
L2PUCPU
SWITCH
SWITCH
SWITCH
LARGE SWITCHDATA COLLECTION NETWORK
SFISFI
Readout Subsystem
ATLAS overall data collection scheme
LVL1
Copyright © 2000 OPNET Technologies, Inc.
Title – 10Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Why trigger on GRID?
•First code benchmarking shows that local CPU power may not be sufficient (budget+ manageable size of the cluster) distribute the work over remote clusters.
•Why not? The GRID technology will provide platform independent tools which perfectly match the needs to run, monitor and control the remote trigger algorithms.
•Developement of dedicated tools (based on the GRID technology) ensuring quasi real-time response of the order of a few seconds might be necessary task for CROSSGRID
Copyright © 2000 OPNET Technologies, Inc.
Title – 11Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Data flow diagram
Experiment Local high level trigger
Tape
Remote high level
trigger
Event buffer for remote
processing
Remote high level
trigger
...decision
decision
Event dispatcher
CROSSGRID
interface
Copyright © 2000 OPNET Technologies, Inc.
Title – 12Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Operational features
• Event dispatcher is a separate module. Easy to activate and deactivate
• Implementation independent on specific trigger solutions for a given experiment
• Dynamical resource assignment to keep system running within assumed performance limits (event buffer occupancy, link bandwidth, number of remote centers, timeout rate...)
• Fault tollerance and timeout management (no decision within allowed time limit)
• User interface to monitor and control by a shifter
Copyright © 2000 OPNET Technologies, Inc.
Title – 13Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Testbed for distributed triggerEasy to test by substituting real experiment data
with PC sending Monte Carlo data
Monte Carlo Data
PC at CERN
Event Buffer
Poland
Spain
Germany
Event Dispatcher - Monitoring and
Control Tool
decision
decision
decision
Copyright © 2000 OPNET Technologies, Inc.
Title – 14Krzysztof Korcyl, Institute of Nuclear Physics, Cracow
Summary
• Trigger systems for the LHC experiments are challenging
• GRID technology may help to solve lack of local CPU power
• Proposed distributed trigger structure as a separate Event dispatcher module offers cross-experiments platform independent of specific local trigger solutions.
• Implementation on testbed feasible even without running experiments
• Dedicated tools to be developed within CROSSGRID project to ensure interactivity, monitoring and control.