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The ATLAS High Level Trigger

The ATLAS High Level Trigger. V é ronique Boisvert CERN On behalf of the ATLAS Trigger/DAQ High Level Trigger Group. Université de Montréal-McGill Seminar August 18 th 2003. Rockefeller Center NY, USA. Outline. Physics Motivation Selection Strategies ATLAS detector LHC environment

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The ATLAS High Level Trigger

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  1. The ATLAS High Level Trigger Véronique Boisvert CERN On behalf of the ATLAS Trigger/DAQ High Level Trigger Group Université de Montréal-McGill Seminar August 18th 2003 Rockefeller Center NY, USA

  2. Outline • Physics Motivation • Selection Strategies • ATLAS detector • LHC environment • Trigger Architectures • High Level Trigger (HLT) Selection Software • Measurements • Conclusions

  3. The Big Questions VLHC 100TeV pp Mu Collider What is the right description Of gravity and where does it Become relevant for particle Physics? Are there more forces? Particles? Symmetries? 0.5-1.0 TeV e+e- Collider Is there unification of all forces? What breaks it? 14 TeV Pp LHC Explain the masses of The p and e, and the Relative strengths of The fundamental forces Nu Factory What breaks EW Symmetry? What is the origin of mass? High Luminosity Z Factory Are there extra Dimensions? What is the structure of spacetime? What is the physics beyond The SM? New particles? New interactions? B,K,tau/charm Factory Flavor Puzzles: Can we understand the masses And mixing of fermions. Where does CP come from? Do we understand the Structure and fate of The universe? Tevatron 2TeV pp Can we explain the universe? Why is it matter dominated? Cosmological Constant? Dark Matter Problem? Particle Astrophysics Adapted from fig. From P. Drell, published in Physics Today Jan 2001

  4. Some Answers from the LHC • Electroweak symmetry breaking • Precise Standard Model measurements • B physics • Physics beyond the Standard Model: • SUSY • Exotics • The unknown!

  5. Electroweak Symmetry Breaking • SM Higgs: • 114.4GeV < mH < 1TeV • LHC Higgs production and cross-sections • Higgs decays: • Fully hadronic: • Large QCD background • Gold plated modes: • H gg • Signature: g pT >= 50GeV/c • s~6 for mH=120GeV, 30 fb-1

  6. Electroweak Symmetry Breaking • Gold plated modes: • H ZZ(*) 4l • Signature: 4 high pT l • s=3-25 (dep. mH), 30fb-1 • Other typical signatures: • tt,bb,lnln,llnn,lljj • MSSM Higgs • Typical signatures for H0, h0, A, H: • tt,mm,tn,tb

  7. Precision Measurements of SM • High Luminosity and High E • LHC is the ultimate factory: • B, top, W, Z, H, … • 1:1013 for Higgs • Deviations from SM • Hints of new physics • Precise W mass • W jj  • Large QCD background • W e(m)n  • n reco. in transverse plane!

  8. Precision Measurements of SM • Precise W mass • Very dependent on E scale (0.02%) • Built-in calibration system • e,m, ATLAS, CMS: DmW~15MeV (today ~34MeV) • Precise Top mass: tt • t Wb Signatures: • Jets (including b-jets), l, Etmiss • All channels, ATLAS, CMS: Dmt~1-2GeV (today ~ 5.1GeV) • Indirect mH~25%! (today ~50%) LHC

  9. B physics • Copious production of B’s: • CP-violation, Bs oscillations, Rare decays, etc. • Bd J/ KS • Max performance: d(sin2b)=0.010 • Min performance: d(sin2b)=0.016 • Rare decays • Forward-Backward A: B0d  K*0m+m- • Lowest mass region: enough accuracy to detect New Physics • Signatures: di-leptons (m), semi-exclusive reconstruction AFB q2/MB2

  10. SuperSymmetry • SM is an effective theory: • Gauge coupling unification (families, gravity, etc.) • Fine-tuning • Hierarchy problem • SUSY: supersymmetric partners s-1/2 • Pros: • Elimination of fine-tuning by exact cancellations between partners • Quark masses: radiative corrections in SUSY • Consistent with string theories (incl. gravity) • Cons: • No observation!  broken, many free parameters and extensions • If weak-scale SUSY exists the LHC experiments will discover it!

  11. ~ c 0 ~ c 0 1 2 ~ ~ qL R q SUSY • MSSM particle spectrum, current limits: • ml, > 90-100 GeV (LEP) • mq,g > 250 GeV (Run 1) • Lightest SUSY Particle (LSP) is 10 • Cold dark matter candidate • Do neutralino reconstruction! • Signature: ETmiss • Decay chains • No SM background, 2-body kinematics • Need jets, l, ETmiss

  12. Beyond the SM • SUSY, Technicolor, Little Higgs, New fermions and gauge bosons, compositeness,… • Large Extra Dimensions • Solves hierarchy problem: • 1 fundamental scale: EW scale (TeV) • Gravity is weak because propagate in 3+n dimensions • Cosmological implications • Constraints from astrophysics • Possible explanation for dark matter • Etc. • Tests Gravity and String Theory in the lab! bulk 3-brane

  13. Beyond the SM • n2: ADD • Graviton emission • Signature: jet(g) + ETmiss • Randall-Sundrum: • n=1 • Warped • 2 branes (Planck and TeV) • Radion: represents fluctuations of the distance between the 2 branes • Signature: Higgs like • Mini black holes! Gr r

  14. So far… • With a little bit of luck the LHC could completely revolutionize our field! • Highlighted possible signatures • Other constraints on the trigger architecture?

  15. The LHC at CERN From: P. Sphicas 2003

  16. The LHC environment • Interaction rate: L x s(pp) = 1034cm-2 s-1 x 70mb = 107mb-1 Hz x 70mb = 7x108Hz! • ~3600 bunches in LHC • Length of tunnel is 27Km • Time between bunches: 25ns!(40MHz bunch x rate)

  17. The LHC environment • Interactions per crossing: ~23! • Minimum bias events overlap each event of interest • We have “pile-up” • “In-time”: particles from same crossing but different pp interaction • “Out-of-time”: left-over signals from previous crossings • Need bunch crossing identification

  18. 22 m 44 m Time of flight… Weight: 7000 t ~108 channels (~2 MB/event)

  19. pp collisions at high luminosity HZZ  4m

  20. T/DAQ challenges • efficient signal selection and excellent background rejection • Interaction rate: 7x108 Hz • Store data at 100 Hz • Bunch crossing rate: 40MHz • Out of time Pile-up • Synchronization over detectors • High number of channels at high occupancy • It’s online!! • If event is not selected it’s lost forever!

  21. Selection Strategies • 2 main guiding principles: • Inclusive selection • Mostly 1 or 2 objects (electron, muon, photon, jet, b-tagged jet, tau, ETmiss, ET) • High pT: > O(10GeV/c) • Worry about: • Low mass objects (eg B physics) • Exclusive selection, topology, etc. • Biases in selection • Use complementary selections

  22. Selection Strategies

  23. So far… • The LHC environment is brutal to a Trigger DAQ system • How to get the job done: • Trigger Architecture

  24. 40 MHz 2.5 ms 75 kHz ~10 ms ~1 kHz ~1 sec ~100 Hz Rate Latency The ATLAS Trigger Architecture Level 1 trigger Region of Interest RoI Level 2 trigger High Level Trigger Event Filter

  25. Introduction: Regions of Interest • Typically a few ROI / event • Ex: Pixel 0.2x0.2 ~ 92 Modules ~ 332 channels • Only few % of event data required!

  26. ATLAS, CMS vs Other detectors

  27. ATLAS vs CMS • ATLAS: • Smaller bandwidth • But more complex • CMS: • Simpler system • But very high bandwidth • dependent on technology

  28. So far… • Introduced ATLAS Trigger Architecture • Let’s look at the HLT Selection Software • Handle to making the Trigger decision • Measurements

  29. HLT Selection principles • Fast • Early rejection • Seeding • Data on demand (RoI or whole event) • Modify easily signatures • Precise knowledge of detectors and algorithms: offline community • Use offline code in the HLT software • Develop Trigger Alg in offline framework • Study boundary between Level 2 and EF • Performance studies for physics analysis

  30. HLT Selection principles • Offline into online: not an easy task! • Requirements of speed and multi-threading on core infrastructure • different steering philosophy: • Offline: typically process entire events in a sequential fashion (post data on a whiteboard) • Online: seeded and early rejection • Appointment of a Reconstruction Task Force • Look at issues regarding offline-online unification • High Level Design (data flow, EDM) • Subdetectors reconstruction • Combined reconstruction • Analysis preparation reconstruction • General Design principles

  31. HLT Design Overview

  32. Package Interface Dependency HLT Selection Software HLT DataFlow Software Event Filter HLTSSW HLT Selection Software Processing HLT Core Software Application Level2 Steering HLT Algorithms Processing Application HLT Algorithms Data Manager ROBData Collector Event DataModel HLTSSW at work: 2e30i

  33. + e30i e30i + e30 e30 e + e Steering ecand ecand + + EM20i EM20i The Steering Signature  • Requirement: • Early rejection • Chosen strategy: • Seeding mechanism • Step wise process Iso lation Iso lation STEP 4 Signature  pT> 30GeV pT> 30GeV STEP 3 Signature  track finding track finding STEP 2 Signature  Cluster shape Cluster shape STEP 1 Level1 seed 

  34. Level1: selects calorimeter info over coarse granularity Level2: 1)cluster E, position, shower-shape variables Refine L1 position: max E (h1, f1) Refine (h1, f1) with Energy weigthed average in window 3x7: (hc, fc) Parameters to select clusters: Sam. 2: Rhshape = E37/E77 Sam. 1: Rhshape = E1-E2/E1+E2 Etotal in 3x7 around (h1, f1) Ehad in 0.2x0.2 around (hc, fc) HLT Algorithms HLT algorithms: e,g selection EM LAr calorimeter ~190,000 channels For 25GeV: sE/E~7%, sq~8mrad, sr~1.6mm

  35. z f h HLT Algorithms HLT algorithms: e,g selection Momentum res.: DpT/pT ~ 0.1 pT (TeV) Impact parameters: srf< 20 mm sz < 100mm • Level 2: • 2) need Track in InDet for el: Pixel, SCT algorithm • Z-finder • Hit Filter • Group Cleaner • Track Fitter

  36. HLT Algorithms HLT algorithms : e,g selection • Event Filter:For electrons passing Level 2, reexamined at EF • Use offline reconstruction algorithms • Calibrated data for the InnerDetector • More tools for reconstruction since full event • Measurements: single el, pT=25GeV/c • Fully simulated events, latest software • Pile-up for low and high lum • Up to date geometry, amount of material, B field

  37. Data Access Byte Stream Converter Data source organized by ROB Data Manager The Data Access Transient EventStore Region Selector Algorithm Trans. Event Store HLT Algorithm Region Selector region list DetElem IDs list DetElem IDs list DetElem IDs ROB ID raw event data DetElems DetElems

  38. Data access granularity Preliminary

  39. Event DataModel The Event Data Model Offline dependencies! • Raw Data in byte stream format • Level1, Level2, EF results, ROB data • Different formats of Raw Data for particular subdetector • RawDataObjects are object representation of Raw Data • For InnerDetector the RDOs are skipped for Level2 (data preparation in converters) • Features • Clusters, Tracks, electrons, jets, etc. • MCTruth info • For debugging and performance evaluation • Trigger Related data • ROI objects, Trigger Type, Trigger Element, Signatures

  40. Package Interface Dependency HLT Selection Software HLT DataFlow Software Event Filter HLTSSW HLT Selection Software Processing HLT Core Software Application Level2 Steering HLT Algorithms Processing Application HLT Algorithms Data Manager ROBData Collector Event DataModel <<import>> <<import>> <<import>> <<import>> Athena/ Gaudi StoreGate Offline Offline Reconstruction Offline Architecture & Core Software EventDataModel Algorithms Offline Reconstruction

  41. Timing Measurements Steering Algorithms Region Selector Data Access

  42. Measurements • Putting it all together in the most realistic environment: the Level 2 Test bed Time[ms] Time[ms]

  43. Conclusions • The LHC: quite a challenge! • The LHC detectors Trigger DAQ systems • Interesting comparisons coming! • The ATLAS architecture • RoI mechanism  • Use of offline code in online environment  • HLT selection software is adequate and performant

  44. From: P. Sphicas 2003

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