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 18 th 2003 Rockefeller Center NY, USA

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

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

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

5. V. Boisvert Electroweak Symmetry Breaking SM Higgs: 114.4GeV < m H < 1TeV LHC Higgs production and cross-sections Higgs decays: Fully hadronic: Large QCD background Gold plated modes: H   Signature:  p T >= 50GeV/c  ~6 for m H =120GeV, 30 fb -1

6. V. Boisvert Electroweak Symmetry Breaking Gold plated modes: H  ZZ(*)  4l Signature: 4 high p T l  =3-25 (dep. m H ), 30fb -1 Other typical signatures: tt,bb,l l,ll,lljj MSSM Higgs Typical signatures for H 0, h 0, A, H  : , , ,tb

7. V. Boisvert Precision Measurements of SM High Luminosity and High E LHC is the ultimate factory: B, top, W, Z, H, … 1:10 13 for Higgs Deviations from SM Hints of new physics Precise W mass W  jj  Large QCD background W  e(  )  reco. in transverse plane!

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

9. V. Boisvert B physics Copious production of B’s: CP-violation, B s oscillations, Rare decays, etc. B d  J/  K S Max performance:  (sin2  )=0.010 Min performance:  (sin2  )=0.016 Rare decays Forward-Backward A: B 0 d  K* 0  +  - Lowest mass region: enough accuracy to detect New Physics Signatures: di-leptons (  ), semi- exclusive reconstruction q 2 /M B 2 A FB

10. V. Boisvert 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. V. Boisvert SUSY MSSM particle spectrum, current limits: m l,  > 90-100 GeV (LEP) m q, g > 250 GeV (Run 1) Lightest SUSY Particle (LSP) is  1 0 Cold dark matter candidate Do neutralino reconstruction! Signature: E T miss Decay chains No SM background, 2-body kinematics Need jets, l, E T miss  qLqL ~    ~ q    ~ R

12. V. Boisvert 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! 3-branebulk

13. V. Boisvert Beyond the SM n  2: ADD Graviton emission Signature: jet(  ) + E T miss 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. V. Boisvert 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. V. Boisvert The LHC at CERN From: P. Sphicas 2003

16. V. Boisvert The LHC environment Interaction rate: L x  (pp) = 10 34 cm -2 s -1 x 70mb = 10 7 mb -1 Hz x 70mb = 7x10 8 Hz! ~3600 bunches in LHC Length of tunnel is 27Km Time between bunches: 25ns! (40MHz bunch x rate)

17. V. Boisvert 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. V. Boisvert Time of flight… Weight : 7000 t 44 m 22 m ~10 8 channels (~2 MB/event)

19. V. Boisvert pp collisions at high luminosity H  ZZ  4 

20. V. Boisvert T/DAQ challenges efficient signal selection and excellent background rejection Interaction rate: 7x10 8 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. V. Boisvert Selection Strategies 2 main guiding principles: Inclusive selection Mostly 1 or 2 objects (electron, muon, photon, jet, b- tagged jet, tau, E T miss, E T ) High p T : > O(10GeV/c) Worry about: Low mass objects (eg B physics) Exclusive selection, topology, etc. Biases in selection Use complementary selections

22. V. Boisvert Selection Strategies Object Examples of physics coverage Nomenclature Electrons Higgs (SM, MSSM), new gauge bosons, extra dimensions, SUSY, W, top e25i, 2e15i Photons Higgs (SM, MSSM), extra dimensions, SUSY  60i, 2  20i Muons Higgs (SM, MSSM), new gauge bosons, extra dimensions, SUSY, W, top  20, 2  10 JetsSUSY, compositeness, resonances j360, 3j150, 4j100 Jet+missing E T SUSY, leptoquarks j60 + xE60 Tau+missing E T Extended Higgs models (e.g. MSSM), SUSY  30 + xE40

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

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

25. V. Boisvert 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. V. Boisvert ATLAS, CMS vs Other detectors

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

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

29. V. Boisvert 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. V. Boisvert 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. V. Boisvert HLT Design Overview

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

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

34. V. Boisvert HLT algorithms: e,  selection Level1: selects calorimeter info over coarse granularity Level2: 1)cluster E, position, shower- shape variables Refine L1 position: max E (  1,  1 ) Refine (  1,  1 ) with Energy weigthed average in window 3x7: (  c,  c ) Parameters to select clusters: Sam. 2: R  shape = E 37 /E 77 Sam. 1: R  shape = E 1 -E 2 /E 1 +E 2 E total in 3x7 around (  1,  1 ) E had in 0.2x0.2 around (  c,  c ) EM LAr calorimeter ~190,000 channels For 25GeV:  E /E~7%,   ~8mrad,  r ~1.6mm HLT Algorithms

35. V. Boisvert HLT algorithms: e,  selection Level 2: 2) need Track in InDet for el: Pixel, SCT algorithm Z-finder Hit Filter Group Cleaner Track Fitter z   Momentum res.:  p T /p T ~ 0.1 p T (TeV) Impact parameters:  r   < 20  m  z < 100  m HLT Algorithms

36. V. Boisvert HLT algorithms : e,  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, p T =25GeV/c Fully simulated events, latest software Pile-up for low and high lum Up to date geometry, amount of material, B field HLT Algorithms

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

38. V. Boisvert Data access granularity Preliminary

39. V. Boisvert The Event Data Model 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 Offline dependencies! Event DataModel

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

41. V. Boisvert Timing Measurements Steering Algorithms Region Selector Data Access

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

43. V. Boisvert 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. V. Boisvert From: P. Sphicas 2003