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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
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Outline Physics Motivation Selection Strategies ATLAS detector LHC environment Trigger Architectures High Level Trigger (HLT) Selection Software Measurements Conclusions
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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 beyondThe 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 theStructure and fate of
The universe?
Are there extraDimensions? What is the structure of spacetime?
What is the right descriptionOf gravity and where does itBecome relevant for particle
Physics?
VLHC100TeV
pp
0.5-1.0 TeVe+e-
Collider
MuCollider
Nu Factory
High LuminosityZ Factory
B,K,tau/charmFactory
Tevatron2TeV
pp
ParticleAstrophysics
14 TeVPp
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
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Some Answers from the LHC Electroweak symmetry breaking Precise Standard Model measurements B physics Physics beyond the Standard Model:
SUSY Exotics
The unknown!
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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 Signature: pT >= 50GeV/c
~6 for mH=120GeV, 30 fb-1
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Electroweak Symmetry Breaking
Gold plated modes: H ZZ(*) 4l
• Signature: 4 high pT l
• =3-25 (dep. mH), 30fb-1
• Other typical signatures:• tt,bb,ll,ll,lljj
• MSSM Higgs• Typical signatures for H0, h0, A,
H:• ,,,tb
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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()• reco. in transverse plane!
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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, Et
miss
• All channels, ATLAS, CMS: mt~1-2GeV (today ~ 5.1GeV)
• Indirect mH~25%! (today ~50%)
LHC
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B physics Copious production of B’s:
CP-violation, Bs oscillations, Rare decays, etc.
Bd J/ KS
• Max performance: (sin2)=0.010• Min performance: (sin2)=0.016
• Rare decays• Forward-Backward A: B0
d K*0 +-
• Lowest mass region: enough accuracy to detect New Physics
• Signatures: di-leptons (), semi-exclusive reconstruction
q2/MB2
AFB
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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!
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SUSY MSSM particle spectrum,
current limits: ml, > 90-100 GeV (LEP) mq,g > 250 GeV (Run 1)
Lightest SUSY Particle (LSP) is 1
0
Cold dark matter candidate Do neutralino reconstruction!
Signature: ETmiss
Decay chains No SM background, 2-body
kinematics Need jets, l, ET
miss
ml
qL~
~
q
±l ±l
~
R
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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
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Beyond the SM n2: ADD
Graviton emission Signature: jet() + ET
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
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So far…
With a little bit of luck the LHC could completely revolutionize our field!
Highlighted possible signatures Other constraints on the trigger architecture?
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The LHC at CERN
From: P. Sphicas 2003
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The LHC environment Interaction rate: L x (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)
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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
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Time of flight…
Weight: 7000 t 44 m
22 m
~108 channels (~2 MB/event)
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pp collisions at high luminosity
HZZ 4
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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!
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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
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Selection Strategies
ObjectObject Examples of physics coverageExamples of physics coverage NomenclatureNomenclature
ElectronsHiggs (SM, MSSM), new gauge
bosons, extra dimensions, SUSY, W, top
e25i, 2e15ie25i, 2e15i
PhotonsHiggs (SM, MSSM), extra
dimensions, SUSY60i, 260i, 220i20i
MuonsHiggs (SM, MSSM), new gauge
bosons, extra dimensions, SUSY, W, top
20, 220, 21010
Jets SUSY, compositeness, resonances j360, 3j150, 4j100j360, 3j150, 4j100
Jet+missing ET SUSY, leptoquarks j60 + xE60j60 + xE60
Tau+missing ETExtended Higgs models (e.g. MSSM),
SUSY30 + xE4030 + xE40
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So far…
The LHC environment is brutal to a Trigger DAQ system How to get the job done:
Trigger Architecture
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The ATLAS Trigger Architecture
40 MHz
75 kHz
~1 kHz
~100 Hz
~1 sec
~10 ms
2.5 s
Rate Latency
Level 1Level 1triggertrigger
Hig
h L
evel Tri
gger
Hig
h L
evel Tri
gger Level 2Level 2
triggertrigger
EventEventFilterFilter
Reg
ion
of
Inte
rest
RoI
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Introduction: Regions of Interest Typically a
few ROI / event Ex: Pixel 0.2x0.2
~ 92 Modules ~ 332 channels
Only few % of event data required!
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ATLAS, CMS vs Other detectors
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ATLAS vs CMS ATLAS:
Smaller bandwidth But more complex
CMS: Simpler system But very high
bandwidth dependent on
technology
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So far…
Introduced ATLAS Trigger Architecture Let’s look at the HLT Selection Software
Handle to making the Trigger decision Measurements
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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
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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
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HLT Design Overview
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HLT Selection Software
HLTSSW
Steering
ROBDataCollector
DataManager
HLTAlgorithms
Processing Application
EventDataModel
Processing Application
Interface
Dependency
Package
Event Filter
HLT Core Software
HLT Algorithms
Level2
HLT Selection Software
HLT DataFlow Software
HLTSSW at work: 2e30i
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The Steering
Requirement: Early rejection
Chosen strategy: Seeding mechanism Step wise process
Isolation
pT>30GeV
Cluster shape
trackfinding
Isolation
pT>30GeV
Cluster shape
trackfinding
EM20i EM20i+
e30i e30i +
e30 e30+
e e +
ecand ecand+
Signature
Signature
Signature
Signature
Level1 seed
STEP 1
STEP 4
STEP 3
STEP 2
Steering
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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 = 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
HLTAlgorithms
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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.: pT/pT ~ 0.1 pT (TeV)
Impact parameters: r< 20m z < 100m
HLTAlgorithms
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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 Fully simulated events, latest software Pile-up for low and high lum Up to date geometry, amount of material, B field
HLTAlgorithms
Trigger Step Rate (Hz) Efficiency (%)Level2 Calo 2114±48 95.9±.3
Level Tracking 59 ±4 88. ±.5Level Matching 37 ± 86.6 ±.6
EF Global 3 ±5 79. ±.7
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The Data Access
Algorithm RegionSelector
HLT Algorithm
RegionSelector
Trans.EventStore
Data Access
ByteStream
Converter
Data sourceorganized
by ROB
TransientEventStore
region
list DetElem IDs
ROB ID
raw event dataDetElems
list DetElem IDslist DetElem IDs
DetElems
DataManager
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Collection Number Number of ROBsPixel module 1744 81SCT side of module 8176 256TRT straw layer 19008 256LAr Trigger Tower 7168 768Tile module 256 32Muon MDT chamber 1168 192Muon CSC chamber 32 32Muon RPC chamber 574 32Muon TGC chamber 1584 32
Data access granularity
Preliminary
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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!
EventDataModel
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HLT Selection Software
HLTSSW
Steering
ROBDataCollector
DataManager
HLTAlgorithms
Processing Application
EventDataModel
Processing Application
Interface
Dependency
Package
Event Filter
HLT Core Software
HLT Algorithms
Level2
HLT Selection Software
HLT DataFlow Software
StoreGateAthena/Gaudi
<<import>><<import>>
Offline Architecture &Core Software
Offline Reconstruction
Algorithms
<<import>>
Offline Reconstruction
<<import>>
Offline EventDataModel
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Timing Measurements
Timing on 2GHz machineLevel2 Calo ~2msLevel2 Tracking ~3ms~EF ~0.5s
Steering
Algorithms
Region Selector
Data Access
1GHz, 3 seeds: 1.2ms
Infrastructure: ~23s :Data access Muons <8 ( )ms GHz
/Lar Tile < ( )ms GHzInnerDetector improvements underway
1GHz, Tile: 0.03ms, Pixel:0.2ms, TRT:1.1ms
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Measurements Putting it all together in the most realistic
environment: the Level 2 Test bed
Time[ms] Time[ms]
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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
V. Boisvert From: P. Sphicas 2003