“Steering the ATLAS High Level Trigger”
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Transcript of “Steering the ATLAS High Level Trigger”
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“Steering the ATLAS High Level Trigger”
COMUNE, G. (Michigan State University) GEORGE, S. (Royal Holloway, University of London)HALLER, J. (CERN)MORETTINI, P. (I.N.F.N. Genova)SCHIAVI, C. (University of Genova & I.N.F.N. Genova)STAMEN, R. (Institute of Physics, University of Mainz)TAPPROGGE, S. (Institute of Physics, University of Mainz)
Computing in High EnergyAnd Nuclear Physics13-17 February 2006
T.I.F.R. instituteMumbai, India
Thanks to the ATLAS collaboration
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Outline
• LHC, ATLAS and ATLAS Trigger• Steering• Seeded and stepwise reconstruction• Configuration and operations• Persistency• Status and timing• Conclusions
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LHC and ATLAS• LHC: 14 TeV CoM p-p collider (@ 40MHz)• High(Low) luminosity regimes: 1034 cm-2/s (2∙1033)
– High(Low) luminosity ~23(2) p-p collisions
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ATLAS Trigger• Event size ≈ 1.5 MB • @ 40MHz => 60 TB/s!!• O(100MB/s) to tape• A three levels Trigger that
only uses “Regions of Interest” (of high pT activity) (RoI)
• Data access/preparation and reconstruction only done for a small fraction of the full event
• Full event building done only at much lower rate
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Offline/Online portability• Complete off/online portability of HLT SW is
guaranteed by reusing offline software in the online system– Level-2 algorithms are custom written
• Use the same services and tools provided by the offline community
– Event Filter algorithms are imported directly from the offline reconstruction code
• adapted to the RoI guided reconstruction • Data converters provide the ability to run
unmodified code against online and offline event data
• Everything in the HLT SW and more specifically in the Steering is designed to allow complete offline/online symmetry– Trigger optimization, building of efficiency Vs rejection
curves, develop trigger strategies and physics menu tables, testing and timing can be done offline
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High Level Trigger Selection SW
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Steering• The Steering is responsible for:
– Unpacking the Level-1/Level-2 Result and creating the initial RoIs/seeds
– Sequencing the PESA algorithms according to static config and dynamic trigger conditions
– Accepting/rejecting events based on a static configuration and the dynamic event reconstruction outcome
– Provide data navigation and persistency tools to the algorithms for seeding and offline purposes
– Forming and handling event result• The Steering has been designed to cope
with the 10ms Level-2 latency
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Seeded & Stepwise Reconstruction• Reconstruction is “initiated” at Level-2 by the Level-1 Regions
of Interests .• Event Filter starts off the Level2 result• The “outcome” of one “Trigger Algorithm” is the “seed” for the
subsequent algorithm• Reconstructed objects in a RoI are “linked” through
“navigational” links among them and back to the initial RoI • Reconstruction is broken down in “steps”
– Which algorithms run at what time is driven by a static configuration (“sequences” objects) matched against the dynamic event outcome (“satisfied” trigger conditions)
• Events can be rejected at any step– Reject/accept is driven by the static configuration
(“signatures/menus” objects) matched against the outcome
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Reconstruction Chain
time
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• The Trigger system is complex:– Hundreds of trigger items: single and multiple channels, combined triggers, pre-scaled
triggers• One must be able to change pre-scale during an LHC run
– In a predictable fashion• Must be able to study trigger signatures efficiencies
– Changing one pre-scale/threshold should not affect the whole system performance!!
• An “entangled” system is hard to operate and to understand• A coherent and disentagled configuration enforced by SW tools
– Allows to disentangle signatures and to easily pinpoint hot triggers– Changes to one signature do not affect the overall Trigger performance
Configuration and operations
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Persistency• Trigger objects are recorded permanently
– For debuging, monitoring, calibration, tuning of physics analyses or selection strategies
• Two technologies are provided– Generic serializer (dictionary based)– Hand written serializer
• For offline:– Trigger optimization and tuning– Trigger algorithms and strategies development– Trigger aware physics analyses
• Completeness • For online:
– Level-2 => Event Filter seeding• Speed
– Event Filter => Storage• Completeness
• The Steering and the Persistency technologies have been developed to enable the development of online triggers in an offline environment using exactly the same SW
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Status and Timing• The development of the Steering is well underway• Software used in the Test Beam, detector commissioning
and large scale MC data productions • Last missing features currently under development
– Topological triggers– Secondary RoIs – Pre-scaled Triggers
• The performance of existing software is well withing the Level-2 latency
100 signatures6 sequencesEvent Result formation
Pentium4 2.8 GHz
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Conclusions• The specifications and high level
design of the Steering software is completed
• Implementation is advanced with positive timing results
• Work is ongoing to add remaining functionalities
• Focus is on the commissioning of the system and on providing the final tools to perform Trigger aware physics analyses