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 – 2 Krzysztof 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 – 3 Krzysztof 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 – 4 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow The ATLAS LHC Experiment

Copyright © 2000 OPNET Technologies, Inc. Title – 5 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow The LHCb LHC Experiment

Copyright © 2000 OPNET Technologies, Inc. Title – 6 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow The LHCb LHC Experiment - an event signature

Copyright © 2000 OPNET Technologies, Inc. Title – 7 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow Challenges for Trigger/DAQ system The challenges: unprecedented LHC rate of 10 9 interactions per second large and complex detectors with O (10 8 ) 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 (m H  100 GeV) rate is ~ of LHC interaction rate Approach: three level trigger system

Copyright © 2000 OPNET Technologies, Inc. Title – 8 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow ATLAS Trigger/DAQ - system overview CALO MUON TRACKING LVL1 Pipeline memories Regions of Interest LVL2 Event builder Data Recording Readout Driver 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: throughput 4 GB/s rate : 100 Hz latency: 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 – 9 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow EF SUBFARM ROS ROD ROS DFM L2SV RolB LVL2 FARM EF SUBFARM SFI L2PU CPU SWITCH LARGE SWITCH DATA COLLECTION NETWORK SFI Readout Subsystem ATLAS overall data collection scheme LVL1

Copyright © 2000 OPNET Technologies, Inc. Title – 10 Krzysztof 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 – 11 Krzysztof 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 Event dispatcher CROSSGRID interface

Copyright © 2000 OPNET Technologies, Inc. Title – 12 Krzysztof 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 – 13 Krzysztof Korcyl, Institute of Nuclear Physics, Cracow Testbed for distributed trigger Easy 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

Copyright © 2000 OPNET Technologies, Inc. Title – 14 Krzysztof 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.