1. 1 John Baines Commissioning of the ATLAS High Level Trigger

2. 2 Overview of Talk ATLAS LHC Parameters The ATLAS Trigger UK & RAL involvement Commissioning – System Tests – Single Beam – Cosmics Successes & Lessons Learned Commissioning in 2009 Summary Material taken from conference talks by: S. Farrington, C. Padilla, R.Hauser, F. Winklmeier, W. Wiedenmann, R. Goncalo, A. Ventura

3. 3 The ATLAS Detector

4. 4 LHC Parameters - Example signal & background rates: 100 GeV Higgs: ~0.1 Hz SUSY <1 Hz W ~500 kHz Z ~80 kHz Background Inelastic: ~1GHz Jets >1kHz Bunch crossing interval : 25ns (40MHz) No. overlapping events : 23 => event rate ~ 1GHz Average no. particles : 1400 About 10 8 channels to read out. ➔ Event size: 1.5 Mbyte ➔ Larger during special runs: > 15 Mbyte ➔ Tier0/Reconstruction/Grid/Storage: output limit about 200 Hz/300 MByte/s Parameters at full luminosity (L=10 34 cm -2 s -1 )

5. 5 Trigger Architecture - Level 1 Level 2 Event Filter 75kHz 2 - 3kHz 200Hz pp 40MHz Calorimeter or Muon (or TRTfastOR) Hardware: FPGA, ASIC Identify Regions of Interest for HLT Software Trigger, commodity PCs Seeded by L1 ROI Full detector granularity. Requests data in RoI from Read Out Buffers Software Trigger, commodity PCs Seeded by L1 & L2 Has access to entire event. 2.5  s 40ms 2GHz CPU 4s 2GHz CPU

6. 6 ATLAS Trigger & DataFlow ~40ms ~4s

7. 7 ATLAS UK HLT RAL: Fred Wickens Monika Wielers Dmitry Emeliyanov Julie Kirk Bill Scott John Baines Student: Rudi Apolle Manchester Oxford Royal Holloway RAL UCL Trigger Selection Software Inner Detector Trigger Electron/photon Trigger B-Physics Trigger Trigger Release Coordination Trigger Validation Trigger Hardware & Farms

8. 8 Level-1 3 sub-systems: L1- Calorimeters L1- Muons Central Trigger Processor (CTP) Signature Identification e/ ,  /h, jets, μ Multiplicities per p T threshold Isolation criteria Missing ET, total ET, jet ET CTP Receive and synchronize trigger information Generate Level-1 trigger decision (L1A) Deliver L1A to other subdetectors Sends the Regions of Interest to the Level 2 trigger

9. 9 The HLT Farm Ultimately: 2300 processors (L2+EF) Now: ~1600 processors

10. 10 Multi-core processors Resource requirements are multiplied with number of process instances Memory ~ 1–1.5 GByte/Application file descriptors network sockets, number of controlled applications ~ 7k presently ~ 20k final systemTrigger

11. 11 HLT Framework Level-2 – HLT selection software runs in the Level-2 Processing Unit (L2PU). – Selection algorithms run in a worker thread. Event Filter(3 kHz→200 Hz) – Independent Processing Tasks (PT) run selection software on Event Filter (EF) farm nodes HLT Event Selection Software is based on the ATLAS Athena offline Framework HLT framework interfaces the HLT event selection algorithms to online Driven by run control and data flow software Event loop managed by data flow software Allows HLT algorithms to run unchanged in the trigger and offline environment

12. 12 HLT Selection Software LVL2: Reduce rate from up to 75 kHz to 2-3kHz in av. 40ms  Custom algorithms with some offline components EF: Reduce rate from 2-3 kHz to 200-300Hz in av. 4s.  Offline algorithms run from HLT-specific wrappers HLT: Processing in Region of Interest  Only process ~few % of event  At LVL2, request data over network for few % of event Early rejection – stepwise processing to minimize execution time for rejected events

13. 13 match? RoI-based, stepwise processing : e/  example EMROI L2 calorim. L2 tracking cluster? E.F.calorim. track? E.F.tracking track? e/  OK? Level 2 seeded by Level 1 Fast reconstruction algorithms Reconstruction within RoI Level1 Region of Interest is found and position in EM calorimeter is passed to Level 2 Ev.Filter seeded by Level 2 Offline reconstruction algorithms Refined alignment and calibration Event rejection possible at each step Electromagnetic clusters e/  reconst.

14. 14 Trigger Menus Trigger Menu defines chains of processing steps starting from LVL1 RoI Menu specified in terms of signatures e.g. mu6, e10, 2j40_xe30 etc. Chains can be prescaled at Level-1 or the HLT Signatures assigned to inclusive data-streams: – egamma, jetTauEtmiss, muons, minbias, Lar and express Example of electron signatures

15. 15 B-physics Triggers

16. 16 Trigger Rates & Streams

17. 17 Commissioning System tests with simulated & previously recorded cosmic data – Download data to Read Out Buffers  Can test with collision events  Exercise system at max. LVL1 rate Cosmic tests: – Individual detectors (“slice weeks”) – Combined runs => Expose algorithms to real detector noise, data errors etc. Beam: – Single beam – Collisions

18. 18 System Tests with simulated data

19. 19 Single Beam - Single beam configuration – injection energy protons circulating in LHC On collision with a collimator, a spray of particles entered the detector Online Offline 10:19 10/9/2008

20. 20 Level-1 Commissioning in Single Beam - Each trigger component needs to be synchronised with the beam pick up -10 10 -88 Bunch crossing

21. 21 Commissioning with Cosmics

22. 22 Cosmic Event

23. 23 Differences in Cosmic v. Beam running No beam clock Muon trigger chambers provide timing Phase issues in read-out of TRT (straw detector) & Muon Drift Chambers No beam/no IP Tracks distributed over d0, z0 L2 dedicated algorithms for fast muon reconstruction (in MDTs) and fast tracking algorithms in inner detector optimized for trajectories pointing towards the beam line Muons in HLT The r-z view could not be fully reconstructed at L2 because algorithms are designed for pointing tracks and data access request is in trigger towers pointing to the IP Possible to relax pointing requirements to study rejection/efficiency Timing issues cause percent-level loss Tracking Level-2 algorithms optimized for tracks from Interaction Point

24. 24 Calorimeter in e/  &  Triggers Study of performance of clustering algorithm in Tau trigger

25. 25 e/  Example plot from e  FEX algorithms comparing L2 and EF: Shower shape in 2nd EM sampling R η =E(3×7)/E(7×7).

26. 26 Muon Trigger  =0.007  =17mRad

27. 27 Muons in the Tile Calorimeter  between tile cluster and ID track

28. 28 Commissioning the InDet trigger Want to commission the LVL2 collisions algorithms with cosmic. But speed-optimisation of Level-2 algos means they are inefficient for tracks more that a ~5 mm from the nominal beam position. Three strategies: 1)Use only the small fraction of events that pass close to the I.P. 2)Loosen cuts in Pat. Rec. (not possible for all Algs.) 3)Shift points.

29. 29 Commissioning Level-2 tracking Add an initial step that applies a shifts to all the points, so the track seems to come from the Interaction Point

30. 30 Level-2 ID Efficiency w.r.t. Tracks reconstructed offline

31. 31 Cosmics for ID alignment HLT trigger used to select events passing through the ID, sent to the the IDCosmic stream & used for offline alignment

32. 32 Commissioning with Cosmics 216 millions events 453 TB data 400k files several streams

33. 33 Data Streaming

34. 34 Online Handling of Time-Out Events Time-out Events go to the DEBUG stream The events are re-processed and streamed as if they had been processed online. The only difference is the file name. Files registered to the corresponding offline DB and processed normally, producing ESD, AOD, etc., but still be separated and with the “recovered” tag.

35. 35 Successes & Lessons learnt Some highlights: Trigger ready for First Beam Single beam events triggered with LVL1 & HLT streaming based on Level-1 HLT run offline on the CERN Analysis Farm Trigger including HLT algorithms exercised in cosmic running ~2 months running, 220 million events incl. long runs of >2M events Successfully streamed events incl. IDCosmic stream used for alignment. Exercised processing of events from the Debug stream Exercised procedures for evaluating new menus & code fixes on CAF prior to online deployment Successfully exercised release management in data-taking conditions deployed patch releases for P1 and HLT

36. 36 Successes & Lessons learned Improvements for 2009 Running: Ability to change LVL1 pre-scales during a run was invaluable  put in place infrastructure to enable HLT prescales to also be updated during run Change of magnetic field required a menu change: => Algorithms now able to configure magnetic field automatically based on magnet current Problems with calculating online Level-2 & EF trigger rates – Old system too susceptible to problems collecting information from farm nodes. – Improvements in rate calculation and collection of information from nodes Removal of detectors from readout caused errors in HLT => events in debug stream – Allow algorithms to access Mask saying which detectors are in the run => modify error response Problems with noisy detectors – Consolidate procedures for making noisy detector masks available online – Improve monitoring, especially detector & trigger info. displayed side-by-side

37. 37 Plans for 2009/10 Luminosity : ~2x10 32 Integrated : ~200pb -1

38. 38 Collisions - Cosmics Cosmics with combined L1 muon triggers First beam menu: Cosmics + beam pickup trigger Bunch groups commissioned (requires clock commissioning) High Level Trigger performs streaming HLT algorithms run offline Add HLT one piece at a time in tagging mode Switch on HLT rejection after algorithms validated online Full 10 31 Menu

39. 39 Collisions - Cosmics Cosmics with combined L1 muon triggers First beam menu: Cosmics + beam pickup trigger Bunch groups commissioned (requires clock commissioning)

40. 40 Collisions - Cosmics Cosmics with combined L1 muon triggers First beam menu: Cosmics + beam pickup trigger Bunch groups commissioned (requires clock commissioning) High Level Trigger performs streaming HLT algorithms run offline Add HLT one piece at a time in tagging mode Switch on HLT rejection after algorithms validated online Full 10 31 Menu

41. 41 Conclusion The trigger was successfully commissioned in Single Beam and Cosmic running in Autumn 2008 Data has been analysed to validate the trigger operation. Improvements have been made in the light of experience from these runs Eagerly awaiting collisions!!

42. 42 Backup Slide

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46. 46 High Level Trigger -

47. 47 Level 1 Cosmic Rates -