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ATLAS Trigger Development

ATLAS Trigger Development. Corrinne Mills Harvard DOE Review August 14-15, 2008. The ATLAS Trigger System. Level One hardware: calo + muon (75 kHz). triggers. Level Two software: partial reco. (3.5 kHz). Region of Interest Builders. triggers. Event Filter software: full reco.

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ATLAS Trigger Development

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  1. ATLAS Trigger Development Corrinne Mills Harvard DOE Review August 14-15, 2008

  2. The ATLAS Trigger System Level One hardware: calo + muon (75 kHz) triggers Level Two software: partial reco. (3.5 kHz) Region of Interest Builders triggers Event Filter software: full reco. (200 Hz) Event Builder to tape c. mills

  3. The ATLAS Trigger System SCT and pixel data Fast TracKer (FTK) (proposed) Level One hardware: calo + muon (75 kHz) triggers triggers Level Two software: partial reco. (3.5 kHz) tracks Region of Interest Builders High Level Trigger (HLT) triggers Event Filter software: full reco. (200 Hz) Event Builder to tape c. mills

  4. A Fast Tracker for ATLAS • “Free” tracks at start of Level 2 processing • Tracking exists in L2, but strongly limited by bandwidth • Exacerbated by high-luminosity conditions • FTK frees up CPU time for other tasks or more events • Applications: displaced tracks from b hadrons, tau leptons, track-based isolation for leptons • Ongoing R&D project • Harvard (Franklin, Mills, Morii) joined last summer • Collaborating institutions: Chicago, Frascati, Illinois, Pisa • Cleared for year-long study leading to TDR in March 2009 • Timeline: installation in 2012 (LHC  SLHC) • Past year: intensive effort to develop and validate simulation c. mills

  5. How does FTK work?

  6. Simplifed Pattern Recognition Group hits into “superhits” (100/ module rather than 100s) particle track c. mills

  7. The Associative Memory Parallel processing • Pre-loaded bank of most probable hit patterns • Dedicated hardware • Look for a match Like a bingo game: c. mills

  8. Linearized Track Finding • Within roads, track-finding problem simplified • Tractable combinatorics • Linear approximations to 2 and track parameter extraction • The Associative Memory associates as set of these linear maps with each pattern • FTK Track finding within road: • Calculate 2 for all permutations of full-resolution hits within road, allowing one layer to have a missing hit • Take hit pattern with best 2, preferentially with no missing layers • Compute track parameters from hit pattern • This step done by DSPs • Output to Level 2 is a list of tracks c. mills

  9. Forward Tracking Performance

  10. Harvard FTK work • Trigger simulation development effort this year • CM extended the trigger simulation to the disks • Simulation software originally developed for the SVT • CDF geometry is purely cylindrical • Tracking looks for hit on each layer • Extend layers forward using the disks • Ideal is to have one hit per “layer” for each track • Difficulty not from software modification, but description of geometry = 2.5 R (mm) z (mm) c. mills

  11. FTK Tracking Efficiency • Efficiency is truth tracks matched to FTK reconstructed tracks, divided by all truth tracks • Theoretical maximum to efficiency: fraction of tracks crossing enough layers eta c. mills

  12. Track Parameter Resolution • Impact parameter (d0) resolution not significantly degraded • b hadrons produce tracks with large d0 (> 0.05 cm) • z0 resolution worsens with dip angle but remains good • Compare to size of interaction region: 10 cm (but many interactions…) • track isolation for leptons c. mills

  13. Other HLT Work

  14. High Level Trigger Event size (~100kB total) • Trigger efficiency measurement • Unified structure to monitor all triggers • Quick turnaround for early data validation • Could develop into working group • “Navigation” structure • Information leading to trigger decision • Ideally store for end user analysis, but: > 10 kB/event, where the whole event is 100 kB or smaller) • Task: trim out unneeded objects • Example: group using high-pT leptons does not need jet trigger details • Short-term project, quick payoff, could lead to more work with HLT group (incl. Navigation) c. mills

  15. Summary and Outlook • Significant contribution to FTK development • Coding and validation of forward tracking in trigger simulation, doubling acceptance • Good tracking efficiency through full pseudorapidity range • Track parameter resolution comparable to central tracks • Cleared for TDR, working toward 2012 installation • Starting up other HLT work • Franklin, Mills, Morii, Smith, potentially more grad students • Potential for real impact on ATLAS performance on a short (~ 1 yr) timescale • Synergy between working knowledge of existing trigger infrastructure and FTK development and integration efforts c. mills

  16. Backup

  17. FTK Architecture Pixels & SCT PIPELINEDAM EVENT # 1 RODs EVENT # N 50~100 KHz event rate HITS Data Formatter (DF) S-links SUPER BINS DATA ORGANIZER TRACK FITTER ROADS cluster finding + split by layer ROADS + HITS Raw data ROBs Track data ROB c. mills

  18. Global Design Considerations Bank size for 1/4 of detector • Tradeoffs: • Road size  bank size • big roads = more computation for track finding (time) • narrow roads = bigger pattern banks / AM (cost) • Efficiency • Minimum reconstructable pT (0.5 GeV? 1 GeV?) 10 boards 1 AM board 2 AM boards c. mills

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