The ATLAS High Level Trigger Vronique Boisvert CERN On behalf of the ATLAS Trigger/DAQ High Level Trigger Group Universit de Montral-McGill Seminar August 18th 2003 Rockefeller Center NY, USA Outline Physics Motivation Selection Strategies ATLAS detector LHC environment Trigger Architectures High Level Trigger (HLT) Selection Software Measurements Conclusions
V. Boisvert The Big Questions Are there more forces? Particles? Symmetries? What is the right description Of gravity and where does it Become relevant for particle Physics? Is there unification of all forces? What breaks it? Explain the masses of The p and e, and the Relative strengths of The fundamental forces Are there extra Dimensions? What is the structure of spacetime? Do we understand the Structure and fate of The universe? V. Boisvert VLHC 100TeV pp
Mu Collider 0.5-1.0 TeV e+eCollider 14 TeV Pp LHC 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? Can we explain the universe? Why is it matter dominated? Cosmological Constant? Dark Matter Problem? Nu Factory High Luminosity Z Factory
B,K,tau/charm Factory Tevatron 2TeV pp Particle Astrophysics Adapted from fig. From P. Drell, published in Physics Today Jan 2001 Some Answers from the LHC Electroweak symmetry breaking Precise Standard Model measurements B physics Physics beyond the Standard Model: SUSY Exotics The unknown! V. Boisvert
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: V. Boisvert H
Signature: pT >= 50GeV/c ~6 for mH=120GeV, 30 fb-1 Electroweak Symmetry Breaking Gold plated modes: Other typical signatures: H ZZ(*) 4l Signature: 4 high pT l =3-25 (dep. mH), 30fb-1 tt,bb,ll,ll,lljj MSSM Higgs Typical signatures for H0, h0, A, H:
V. Boisvert ,,,tb Precision Measurements of SM High Luminosity and High E LHC is the ultimate factory: Deviations from SM B, top, W, Z, H, 1:1013 for Higgs Hints of new physics Precise W mass W jj
Large QCD background W e() V. Boisvert reco. in transverse plane! Precision Measurements of SM Precise W mass Very dependent on E scale (0.02%) Built-in calibration system e,, ATLAS, CMS: mW~15MeV (today ~34MeV) Precise Top mass: tt
t Wb Signatures: Jets (including b-jets), l, Etmiss All channels, ATLAS, CMS: mt~1-2GeV (today ~ 5.1GeV) Indirect mH~25%! (today ~50%) V. Boisvert LHC B physics Copious production of Bs: CP-violation, Bs oscillations, Rare decays, etc. AFB Bd J/ KS Max performance: (sin2)=0.010 Min performance: (sin2)=0.016 Rare decays Forward-Backward A: B0d K*0 + Lowest mass region: enough accuracy to detect New Physics
Signatures: di-leptons (), semiexclusive reconstruction V. Boisvert q2/MB2 SuperSymmetry SM is an effective theory: Gauge coupling unification (families, gravity, etc.) Fine-tuning Hierarchy problem SUSY: supersymmetric partners s-1/2 Pros: Cons:
V. Boisvert Elimination of fine-tuning by exact cancellations between partners Quark masses: radiative corrections in SUSY Consistent with string theories (incl. gravity) No observation! broken, many free parameters and extensions If weak-scale SUSY exists the LHC experiments will discover it! 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 V. Boisvert l ~ q~ L lR
q m ~ l Beyond the SM SUSY, Technicolor, Little Higgs, New fermions and gauge bosons, compositeness, Large Extra Dimensions Solves hierarchy problem: Cosmological implications
1 fundamental scale: EW scale (TeV) Gravity is weak because propagate in 3+n dimensions Constraints from astrophysics Possible explanation for dark matter Etc. Tests Gravity and String Theory in the lab! V. Boisvert bulk 3-brane Beyond the SM n2: ADD Graviton emission Signature: jet() + ETmiss
Gr Randall-Sundrum: n=1 Warped 2 branes (Planck and TeV) V. Boisvert Radion: represents fluctuations of the distance between the 2 branes Signature: Higgs like Mini black holes! r So far
With a little bit of luck the LHC could completely revolutionize our field! Highlighted possible signatures Other constraints on the trigger architecture? V. Boisvert The LHC at CERN V. Boisvert From: P. Sphicas 2003 The LHC environment Interaction rate: L x (pp) = 1034cm-2 s-1 x 70mb = 107mb-1 Hz x 70mb = 7x108Hz! ~3600 bunches in LHC V. Boisvert Length of tunnel is 27Km Time between bunches: 25ns! (40MHz bunch x rate) The LHC environment
Interactions per crossing: ~23! Minimum bias events overlap each event of interest We have pile-up V. Boisvert In-time: particles from same crossing but different pp interaction Out-of-time: left-over signals from previous crossings Need bunch crossing identification Time of flight 22 m Weight: 7000 t V. Boisvert 44 m
~108 channels (~2 MB/event) pp collisions at high luminosity V. Boisvert HZZ 4 T/DAQ challenges efficient signal selection and excellent background rejection Interaction rate: 7x108 Hz Bunch crossing rate: 40MHz Store data at 100 Hz Out of time Pile-up Synchronization over detectors High number of channels at high occupancy
Its online!! V. Boisvert If event is not selected its lost forever! Selection Strategies 2 main guiding principles: Inclusive selection Mostly 1 or 2 objects (electron, muon, photon, jet, btagged jet, tau, ETmiss, ET) High pT : > O(10GeV/c) Worry about: Low mass objects (eg B physics)
Biases in selection V. Boisvert Exclusive selection, topology, etc. Use complementary selections 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, 2i, 220i, 2i Muons
Higgs (SM, MSSM), new gauge bosons, extra dimensions, SUSY, W, top 20i, 2, 210i, 2 Jets SUSY, compositeness, resonances j360i, 2, 3j150i, 2, 4j10i, 20i, 2 Jet+missing ET SUSY, leptoquarks j60i, 2 + xE60i, 2 Tau+missing ET Extended Higgs models (e.g. MSSM), SUSY 30i, 2 + xE40i, 2 V. Boisvert So far
The LHC environment is brutal to a Trigger DAQ system How to get the job done: Trigger Architecture V. Boisvert The ATLAS Trigger Architecture 40 MHz ~10 ms ~1 kH z ~1 sec ~100 Hz Rate V. Boisvert Latency Region of Interest RoI 2.5 s High Level Trigger
75 kHz Level 1 trigger Level 2 trigger Event Filter Introduction: Regions of Interest Typically a few ROI / event Ex: Pixel 0.2x0.2 ~ 92 Modules ~ 332 channels Only few % of event data required! V. Boisvert
ATLAS, CMS vs Other detectors V. Boisvert ATLAS vs CMS ATLAS: Smaller bandwidth But more complex CMS: Simpler system But very high bandwidth V. Boisvert dependent on technology So far
Introduced ATLAS Trigger Architecture Lets look at the HLT Selection Software Handle to making the Trigger decision Measurements 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 V. Boisvert Develop Trigger Alg in offline framework Study boundary between Level 2 and EF Performance studies for physics analysis 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) V. Boisvert Subdetectors reconstruction Combined reconstruction Analysis preparation reconstruction General Design principles HLT Design Overview V. Boisvert HLT Selection Software HLT DataFlow Software Event Filter Processing Application
Package HLTSSW HLT Selection Software HLT Core Software Level2 Steering HLT Algorithms Processing Application HLT Algorithms Data Manager ROBData Collector V. Boisvert Event DataModel HLTSSW at work: 2e30i Interface
Dependency Steering The Steering Signature STEP 4 Requirement: Early rejection Chosen strategy: Seeding mechanism Step wise process V. Boisvert Signature STEP 3 Signature
e30i Iso lation e30 e track finding Signature ecand STEP 1 Cluster shape EM20i e30i Iso lation + pT> 30GeV STEP 2 Level1 seed
+ e30 p T> 30GeV + e track finding + ecand Cluster shape + EM20i HLT Algorithms HLT algorithms: e, selection Level1: selects calorimeter info over coarse granularity
Level2: 1)cluster E, position, showershape variables Refine L1 position: max E (1, 1) Refine (1, 1) with Energy weigthed average in window 3x7: (c, c) Parameters to select clusters: V. Boisvert Sam. 2: Rshape = E37/E77 Sam. 1: Rshape = E1-E2/E1+E2 Etotal in 3x7 around (1, 1) Ehad in 0.2x0.2 around (c, c) EM LAr calorimeter ~190,000 channels For 25GeV: E/E~7%, ~8mrad, r~1.6mm HLT Algorithms
HLT algorithms: e, selection Momentum res.: pT/pT ~ 0.1 pT (TeV) Level 2: 2) need Track in InDet for el: Pixel, SCT algorithm Impact parameters: r< 20m z < 100m Z-finder Hit Filter Group Cleaner Track Fitter V. Boisvert z
HLT Algorithms 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, pT=25GeV/c V. Boisvert Fully simulated events, latest software Pile-up for low and high lum Up to date geometry, amount of material, B field Trigger Step Rate (Hz) Level2 Calo
211448 LevelTraki 59 4 LevelMai 37 3 5 EFGloal Efficiency (%) 95.9 .3 88. .5 86.6 .6 79. .7 Data Manager The Data Access Algorithm Region Selector Transient EventStore HLT Algorithm Region Selector Trans. Event
Store Data Access Byte Stream Converter Data source organized by ROB region list DetElem IDs list DetElem IDs list DetElem IDs DetElems DetElems V. Boisvert ROB ID raw event data Data access granularity Collection Number Number of ROBs Pixel module 1744
81 SCT side of module 8176 256 TRT straw layer 19008 256 LAr Trigger Tower 7168 768 Tile module 256 32 Muon MDT chamber 1168 192 Muon CSC chamber 32 32 Muon RPC chamber 574 32 Muon TGC chamber 1584
32 Preliminary V. Boisvert Event DataModel The Event Data Model Raw Data in byte stream format Clusters, Tracks, electrons, jets, etc. MCTruth info For InnerDetector the RDOs are skipped for Level2 (data preparation in converters) Features
Level1, Level2, EF results, ROB data Different formats of Raw Data for particular subdetector RawDataObjects are object representation of Raw Data Offline dependencies! For debugging and performance evaluation Trigger Related data ROI objects, Trigger Type, Trigger Element, Signatures V. Boisvert HLT Selection Software HLT DataFlow Software Event Filter Package HLTSSW Processing Application HLT Selection Software
~EF ~0.5s Region Selector Data Access V. Boisvert 1GHz, Tile: 0.03ms, Pixel:0.2ms, TRT:1.1ms ~23 Infrastructure: aaae: Muo <8(GHz)) Lar/TileTile <(GHz)) Iereeor iproveeuerwa Measurements Putting it all together in the most realistic environment: the Level 2 Test bed Time[ms] V. Boisvert Time[ms] Conclusions
The LHC: quite a challenge! The LHC detectors Trigger DAQ systems Interesting comparisons coming! The ATLAS architecture V. Boisvert RoI mechanism Use of offline code in online environment HLT selection software is adequate and performant V. Boisvert From: P. Sphicas 2003
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