Post on 30-Jan-2016
description
TRIGGERING IN THE ATLAS
EXPERIMENT
Thomas Schörner-SadeniusUHH (formerly CERN EP/ATR)
UHH, SS06
UHH, SS06 TSS: Triggering in ATLAS 2
OVERVIEW
¶ INTRODUCTION • The Large Hadron Collider (LHC) – Why? • Physics at the LHC • The ATLAS Experiment • The ATLAS Trigger
¶ THE LEVEL1 TRIGGER (L1)
¶ THE HIGH-LEVEL TRIGGER (HLT)
¶ TRIGGER PERFOMANCE STUDIES
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THE LHC - WHY?Standard-Model (SM) well confirmed, but incomplete !
LHC • Higgs bosons (SM/MSSM)• Supersymmetry• Large Extra Dimensions, Compositeness, new heavy gauge bosons• SM measurements, b physics
LEP, HERA,Tevatron …
+ SM precision measurements (QED, QCD, electroweak) -- EW symmetry breaking?-- 25 free parameters?-- Unification?-- Discrepancy at sin2eff etc?
… but openquestions:
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PHYSICS AT THE LHC Ipp collisions with s = 14 TeV,L = 1034 cm-2s-1, f = 40 MHz
SM Higgs:
MSSM/SUSY:
SM Physics:
B0dK0*
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PHYSICS AT THE LHC IIComparison of SM and ‘new physics’ processes
Small cross-sections for
‘new physics’processes
Understandingof SM processes
important
• Backgrounds for ‘discovery physics’: Wbb, ttbb, W/Z pairs…• Calibration, energy scale: Ze+e-,+-, J/e+e-,+-, Wjj…
At high luminosity~23 events overlaid
… for 2•1033cm-2s-1 usually only one event
… and small branching ratios (e.g. H).SM processes dominate.
Necessity of efficient trigger!
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ATLAS TRIGGER MENU COVERAGE
Inclusive anddi-lepton
B physics
H
SUSY,leptoquarks
Resonances,compositeness
• Gauge boson pair production for study of anomalous couplings and behaviour of production at high energies • single and pair top production• direct Higgs production with HZZ*/WW*; associated SM Higgs production with WH, ZH, ttH• MSSM Higgs decays• Production of new gauge bosons with decays to leptons. • SUSY and leptoquark searches
• specialised, more exclusive menus
• 2EM15I at L1, 220i at L2. Also MSSM.
• High pT jets with/without ETmiss.
• High pT jets.
Triggering mostly with inclusive / di-leptons.
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THE LHC pp at 14 TeV
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THE LHC pp at 14 TeV
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THE LHC pp at 14 TeV
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THE LHC pp at 14 TeV
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THE ATLAS EXPERIMENT - Length ~40 m- Diameter ~25 m- Weight ~7000 t- 108 channels (event ~2MB)
- ‘Inner (tracking) Detector’- calorimeters (energies)- muon detectors
- Barrel: solenoid around ID and toroid fields in muon system- Endcaps: toroid fields
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THE ‘INNER DETECTOR’
Pixel Detector:
- 3 barrel layers - 2•4 end-discs - 140•106 channels- R=12m,z,R=~70m- || <2.5
Silicon Tracker:
- 4 barrel layers, || <1.4 - 2•9 end-discs, 1.4 < < 2.5- Area 60 m2
- 6.2•106 channels- R=16m, z,R=580m
Transition Radiation Tracker
- 0.42•106 channels- =170m per straw- || <2.5
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THE CALORIMETERS
Hadronic Tile:
- 463000 scintillating tiles- 10000 PMTs- Granularity 0.1•0.1 - : <1.0, (0.8-1.7)- L=11.4 m, Rout=4.2 m
Hadronic LArEndcaps:
- steel absorbers- 4400 channels- 0.1•0.1 / 0.2•0.2- 1-5
EM LAr Accordeon:
- lead absorbers- 174000 channels- 0.025•0.025- : <2.5, <3.2
Forward LAr:
- 30000 rods of 1mm- cell size 2-5cm2 (4 rods)- : <3.1, <4.9- 1 copper, 2 tungsten
LAr Pre-Sampler
Against effects of energy losses in front
of calorimeters
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THE MUON SYSTEM
Monitored Drift Tubes
- 3 cylinders at R=7, 7.5, 10m- 3 layers at z=7, 10, 14 m- 372000 tubes, 70-630 cm- space=80m, t=300ps (24-bit FADCs)
Cathode Strip Chambers
- 67000 wires- only for ||>2 in first layer- space=60m, t=7ns
Thin Gap Chambers
- 440000 channels- ~MWPCs
Resistive Plate Chambers
- 354000 channels- space=1cm- trigger signals in 1ns
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THE ATLAS TRIGGER: OVERVIEWMulti-layer structure for rate reduction: 1 GHz 100 Hz.
} EF
- Full event- Best calibration- Offline algorithms- Latency ~seconds
} L1
- Hardware-based (FPGAs and ASICs)- Coarse granularity from calo/muon- 2s latency (pipelines)
} L2
- ‘Regions-of-Interest’- ‘Fast rejection’- Spec. algorithms- Latency ~10ms
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OVERVIEW
¶ INTRODUCTION
¶ THE LEVEL1 TRIGGER (L1) • Overview • The Calorimeter and Muon Triggers • The CTP and the L1 Event Decision • Simulation (and Configuration)
¶ THE HIGH-LEVEL TRIGGER (HLT)
¶ TRIGGER PERFOMANCE STUDIES
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THE LEVEL1-TRIGGERSelection based on high-pT objects from calo and muon.
Multiplicities
Regions-of-
InterestEvent decisionfor L1
Interface tofront-end
Muoncandidatesabove pT
thresholds
Interface to highertrigger levels/DAQ:objects with pT,,
Candidates forelectrons/photons,taus/hadrons,jetsabove pT thres-holds.
Energy sumsabove thresholds
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THE CALORIMETER TRIGGER IComplex system with many modules to be developed.
digitisation,presumming to jet
elements with0.2•0.2 granularity
analog sums of EM/HA cells
7200 trigger towers(granularity 0.1•0.1)
cluster processor:Find e/ and /hadron
candidates in 6400trigger towers
(||<2.5)
jet/energy processor:- Find jet candidates in 30•32 jet elements for ||<3.2- Build total ET sum up to ||<4.9.
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THE CALORIMETER TRIGGER II
Example: The /hadron trigger Example: The jet/energy trigger
• 2·2 jet EM+HA cluster (RoI) in 2·2 or 3·3 or 4·4 region (gives ET).
• 8 (4) (forward) jet ET thresholds.
• Total/missing ET from jets (sum of 0.2·0.2 jet elements to ·=0.4·0.2, conversion to Ex,Ey, then summation).
• Maximum of EM+HA ET in 2·2 ‘RoI’, isolation criteria (alternative core definitions?).
• Multiplicities for 8(8) e/ (/ hadron) ET thresholds.
Builds candidate objects (RoIs): electrons/photons, taus/hadrons, jets.Ideas about core definitions, isolation criteria not really finalised.
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THE MUON TRIGGER
• ‘Roads’ can be defined for 6 different pT thresholds (for which multiplicity counts are delivered to the CTP).• BCID=1.5 ns.
Trigger chambers: • 3 RPC stations for ||<1.05• 3 TGC stations for 1.05<||<2.4. • 2 , layers per station (TGC 2/3)
pT information from hit coincidences in successive detector layers.
Procedure:• Put predefined ‘roads’ through all stations (width in ~ pT). • If hit coincidences in 2(3) stations muon candidate for pT thres- hold corresponding to ‘road’.
ATLAS quadrant in rz view
trigger chambers
precision chambers
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THE MUON-TO-CTP INTERFACE208 RPC/TGC sectors deliver 1-2 RoIs combined by 16 MIOCTs.
MIBAK backplane builds RoImultiplicities for 6 pT thresholds.
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THE L1 DECISIONDerived in the ‘Central Trigger Processor’ (CTP).
Multiplicitiesof objects above
pT thresholds
‘Conditions’:multiplicity
requirements
‘Items’: logicalcombinationsof ‘conditions’
L1 result as‘OR’ of all ‘items’
Inputs to HLT: L1 result and objects with pT,,.
CTP
calorimeter, muon
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THE CENTRAL TRIGGER PROCESSOR
existing prototype1 9U VME module
final design~7 different modules
Combines calorimeter and muon information to L1 decision.
Lookup tables:‘conditions’
Programmabledevices: ‘items’
Dead time etc.
Combinationof ‘items’
One big FPGA
Interfaces todetectors,LHC
Input bits: multiplicities
To Level2 Number of items?
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L1 SIMULATION: OVERVIEWMost developments originally for stand-alone applications.
Generation of MonteCarlo events for analysis purposes Rate/efficiency estimates Inputs for HLT tests Tests of L1 trigger hardware (~done for some compo- nents; just starting ‘slices’, configuration problem!)
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L1 SIMULATION: ORGANISATION
Organisation Coordination: TSS Calorimeter trigger: London Muon trigger + MuCTPI: Tokyo, Rom, CERN CTP, RoIB, interfaces, configuration: TSS
Framework C++ Code LHCb framework Gaudi adapted to ATLAS-needs Athena (ATLAS Offline environment)
Status Complete simulation chain for calo trigger ready. Currently working on muon trigger integration. Also done: configuration code (sets up L1 trigger simulation software and hardware !) Successfully used for simulation of L1 result as input to HLT tests (important for HLT TDR).
Many contributors around the world.
Storageconcept
Specific concept for run/event-wise data persistency: StoreGate and DetectorStore for package communication: Objects are sent to predefined memory locations with ‘keys’.
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L1 CONFIGURATIONBased on XML:
<TriggerThreshold name=“MU6” value=“6” bitstart=“3” bitlength=“3” etamin=“-5” …. />
<TriggerThreshold name=“JT90” value=“90” bitstart=“6” bitlength=“3” etamin=“-5” …. /> Calo and muon need to know
which multiplicity is to be delivered on which physical line.
• Simple definition of logical structures (better HTML).• Simple ‘parsing’ into instances of C++ classes.
<TriggerMenu> <TriggerItem> <AND> <TriggerCondition threshold=“MU6” multiplicity=“2” /> <TriggerCondition threshold=“JT90” multiplicity=“1” /> </AND> </TriggerItem></TriggerMenu>
Structure of L1 decision configures CTP.
Prevent from configuring logical structure that exceeds CTP’s abilities (number of inputs etc.).
Definition ofobjects to be
triggered:Trigger Menu
Def. of objectsfor which calo andmuon deliver multi-
plicity counts:thresholds
Description of hardware
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<TriggerMenu> <TriggerItem> <AND> <TriggerCondition threshold=“MU6” multiplicity=“2” /> <TriggerCondition threshold=“JT90” multiplicity=“1” /> </AND> </TriggerItem></TriggerMenu>
L1 CONFIGURATION
Implementationin C++ classes
Logical tree structureof XML tags
Definitions oftrigger menu
“Parsing”
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PROBLEM: HARDWARE CONFIGURATION
Idea: Runsimulation against
L1 hardware
Tests of hardware and software systems. Needs common input data. Needs unified configuration for simulation software and hardware.
Status First lookup table files successfully loaded. First (simple) VHDL code written. Translating and loading dangerous (damaging FPGA).
Have to generate lookup table files VHDL code for FPGAs. Have to be generated ‘on the fly’, from running configuration code.
Problem
TBV[0] = MIO[0] & MIO[1] & !MIO[2] & maskff[0] & !LOCADT[0] & !GLOBDT1[0] & !GLOBDT2[0] & !VETO
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OVERVIEW
¶ INTRODUCTION
¶ THE LEVEL1 TRIGGER (L1)
¶ THE HIGH-LEVEL TRIGGER (HLT) • Design of HLT and Selection Software • Selection Principles and Step-wise Procedure • HLT Decision • HLT Configuration
¶ TRIGGER PERFOMANCE STUDIES
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THE HIGH-LEVEL TRIGGER (HLT)Good example for solid software process.
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HLT: DESIGN OVERVIEW
EventFilter (EF)
ClassificationSelection
~102 Hz
Hardware Implementation
LEVEL 2 (LVL2)
~1 kHzLevel1 (L1)
~102 kHz
Read-OutSubsystemModules
High-Level Trigger: Design
HIGH-LEVEL TRIGGER (HLT)
Offline
Simplified subsystem view
Event- Filter
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HLT: SELECTION SOFTWARE
HLTSSW
Steering Monitoring Service
1..*
MetaData Service
1..*ROBDataCollector
DataManager HLTAlgorithms
Processing Task
EventDataModel
LVL2PU Application
<<import>>
Offline EventDataModel
Offline Reconstruction
Algorithms
<<import>>
StoreGateAthena/Gaudi
<<import>><<import>>
Interface
Dependency
Package
EventFilter
Level2
PESA Core Software
PESA Algorithms
Offline Architecture & Core Software
Offline Reconstruction
Running in Level2 Processing Units (L2PU)+EF.
Set-up by HLT configuration
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HLT: SELECTION PRINCIPLES
‘Regions-of-Interest’ (RoI)
Step-wiseprocess and
‘Fast rejection’
Flexible L2/EF boundary
Use of offlinereconstruction
algorithms
PESA = ‘Physics- and Event Selection Architecture’
¶ Selection/Rejection starts with localized L1 objects (‘Regions-of-Interest’) limited data amount.¶ Then step-wise more and more correlated data from muon/calo and other detectors (e.g. cluster shapes, tracks for e/ separation).
¶ After every step: Check whether selection criteria still fulfilled optimal use of HLT processors.
¶ flexible distribution of load and use of resources.
¶ Use of common software architecture + algorithms understanding of trigger rates/efficiencies. ¶ Use of common ‘event data model’ (should be trivial ;-) ).
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HLT DECISION (LEVEL2 AND EF)Overview of step-wise procedure with ‘dummy’ example Ze+e-
After every step: test + possibly rejection.
‘Physics Signature’: Ze+e- withpT>30 GeV
‘IntermediateSignature’
‘IntermediateSignature’
L1 result: 2 EM clusters
with pT>20 GeV
‘IntermediateSignature’
decision part algorithmic part
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OVERVIEW
¶ INTRODUCTION
¶ THE LEVEL1 TRIGGER (L1)
¶ THE HIGH-LEVEL TRIGGER (HLT)
¶ TRIGGER PERFOMANCE STUDIES • Selection Planning • L1 Performance • L2 / HLT / Combined Performance
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TRÍGGER STUDIES
Mostly done using full GEANT simulation of ATLAS detector and of trigger logic. Usually not full events used, but only parts (QCD jets, H processes etc.) Full dijet event ~1000s.
For jets and ETmiss studies only with fast parametrised simulation. Fast L1 trigger simulation for some purposes (large samples etc.).
Most studies have large uncertainties: LO MCs, computing time per event, costs, classification. Should be reduced with new L1 simulation + HLT software for HLT technical design report (5/2003).
Only rigidly done for L1+L2. EF should be ~100% efficient.Most studies from 1998 Trigger Performance Status Report.
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LEVEL1 SELECTION: PLANNING
Selection 2·1033 cm-2s-1 1034 cm-2s-1
MU6(20?) (20) 23 (3?) 4.0
2MU6 --- (1?) 1.0
EM25i (30) 11 22.0
2EM15i (20) 2 5.0
J200 (290) 0.2 0.2
3J90 (130) 0.2 0.2
4J65 (90) 0.2 0.2
J60+xE60 (100) 0.4 0.5
TAU25+xE30 2.0 1.0
MU10+EM15i --- 0.4
others 5.0 5.0
total ~ 44 (25?) ~ 40
Rates in kHz; thresholds define 95% efficiencies.
No safety factors included (LO MonteCarlos etc.).
Muon triggerscontribute to
(di)lepton signatures.
Electron/photontriggers strong;
large backgrounds.
Low rate for jettriggers; difficult to
control backgrounds
New studies assume much reduced rate (~kHz).
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HLT SELECTION: PLANNING
Selection 2·1033 cm-2s-1 1034 cm-2s-1 Rates (Hz, low lumi)
Electron e25i, 2e15i e30i, 2e20i ~40
Photon 60i, 220i 60i, 220i ~40
Muon 20, 210 20, 210 ~40
Jets j400, 3j165, 4j110 j590, 3j260, 4j150 ~25
jet+Etmiss j70+xE70 j100+xE100 ~20
tau+Etmiss 35+xE45 60+xE60 ~5
B physics 26 with mB/mJ/ 26 with mB ~20
Total ~200
Optimization of efficiency/rejection and CPU load / data volume.
Rate·Event size (1.6MB) needed band widths / storage volumeRate·CPU time number of processors (500?)
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threshold ~30 GeV
Inclusive e/ triggerrate for high lumi
with/without isolation.
L1 e/ TRIGGER
SelectionThreshold[ET in GeV]
Rate[kHz]
1 e/ 17 / 26 11 / 21.5
2 e/ 12 / 15 1.4 / 5.2
Total rate 13 / 27
threshold ~20 GeV
e/ pair trigger ratefor high lumi with/without isolation.
EM isolation for e/jets
Tolerable rate dictates ET thresholds. Isolation criteria vital for rate control.
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L1 /hadron TRIGGER
25 GeV threshold, but no single tau / hadron trigger planned for (hadr. decays HA calibration?).
Selection EM Isolation Rate
20 GeV 7 GeV 16 kHz
40 GeV 10 GeV 2.1 kHz
25 GeV+ETmiss 1-2 kHz
L1 tau/hadron efficiency as function of tau pT.
Problems:- Core definition (2•1,2•2,2•2+4•4 etc.)- isolation threshold definition.
For Z, W with additional lepton or ETmiss.
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L1 JET TRIGGER: 1,3,4 JETS
Efficiency to flag a jet RoI at high lumi.How low can you go?
Type Low lumi High lumi
1 jet ET>180GeV ET>290GeV
3 jets ET>75GeV ET>130GeV
4 jets ET>55GeV ET>90GeV
Rate assigment defines thresholds and jet windows.
Performance depends on- window for ET determination,- jet element thresholds, - declustering procedure.
Njet=1
Njet=4180 GeV
55 GeV
Jet trigger rates (low lumi), assign 200Hz for 1,3,4 jet processes
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L1 MUON TRIGGER PERFORMANCE
TGC efficiency for different thresholdssharp rise, good .
Type Barrel Endcap All Non-pp
6 GeV 10 13.2 23.2 >0.4
20 GeV 1 2.8 3.8 >0.026
Mainly want to trigger W/Z. Semilept.b,c is background (L2).
Fake rates from backgroundparticles about 10Hz/cm2? Newmuon studies assume less rate.
Muon trigger rates overview [kHz]
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HLT: CALORIMETER TRIGGERS
Second sampling(0.025•0.025):
24X0
Back sampling(0.05•0.025): 2-12X0
• Main backgrounds in L1 sample: 0 and narrow hadronic jets.• Algorithms mainly based on ET, hadronic leakage, lateral shower shape and sub-structures in cluster (use of track veto possible).
Variables:- EM-ET in 3•7 cells E=wgl(wps*Eps+E1+E2+E3)- HA-ET
- lateral shape in 2. sampling: R = E3*7 / E7*7 >0.9 for e- lateral shape in 1. Sampling for narrow hadr. showers or jets with small Ehad
- Cuts tuned for >0.95 with large jet rejections
First sampling with finer cell granularity for 0 rejection
(0.003•0.1): 6X0
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HLT TRIGGER: 40(60)i, 220i
2 peaks from0 / narrowhadronic shower
from jet BG(first sampling)
1 peak fromreal
Validation of L1 ET,, information (granularity, calibration) sharper cuts on ET + cluster shape analysis.
Efficiency for 20 GeV photons at high lumi.
Single photon efficiency > 90% (diphoton triggers >80%; f(ET)).
100 (600) Hz on L2 for triggers.Jet rejection of ~3000.
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HLT ELECTRON: e25(30)i, 2e15(20)iSimilar to photons, but looser cuts. Track search in inner detector (reject neutrals, cuts on pT, shower shapes etc.).
L2 e/ triggerefficiency for
30 GeV electrons,(high lumi).
Electron triggers: rate of 100 (600) Hz after L2 selection.
Service crack betweenbarrel and endcap
Efficiency afterL1+L2 for single30GeV electrons
at high lumi.
Crack betweenbarrel halves
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HLT JET TRIGGER: 1,3,4 JETS
L2 jet efficiency for50,100,150 GeV asfunction of threshold(cone, threshold fromtrigger jet).
L2/L1 reduction forlow lumi at 90(95)%
L2(L1) 1-jet efficiency(2 at 80 GeV).
Hard to suppress BG without inv. Mass cuts. Sum cells to 0.1•0.1; run jet algo on 1.0•1.0 window around RoI.
Type L1 [kHz] L2 [kHz]
J180 0.2 0.12
3J75 0.2 0.08
4J50 0.2 0.04 Rates for =95(90)% L1(L2).
Algorithms? Cell noise cut?Threshold definition? Window size?
L1 TT cut 1 GeV
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• Get pT(MDTs), extrapolate track• Reduce L1 rate by ~100 (harder
cuts or more subdetectors)• Reduce BG from b-decays by factor 10 with high W/Z- 95%.
HLT MUON TRIGGER: 20, 210
L2 trigger algorithmefficiency in barrelfor two thresholds.
Efficiency >95% with r.m.s momentum resolution of 1-2 GeV (7% for 6 GeV)).
--- W,Z signal • b,c BG
Also ET criteriain calo cones
200(300) Hz L2 trigger rate for signatures (without B triggers with
exclusive requirements on masses).
Calo discriminatesW/Z vs. b,c.
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SUMMARY
LHC/ATLAS• Necessary to complete Standard Model and to find extensions (SUSY etc.).• High event rates + small new physics cross-sections.• Multi-layer structure: Reduction 1 GHz 100 Hz.
L1 Trigger• Hardware-based with calo/muon inputs.• L1 decision in Central Trigger Processor (CTP).•(Offline) configuration and simulation ~ready.
HLT• HLT: Two software levels (Level2 and EventFilter)• HLT principles: Regions-of-Interest and step-wise decision procedure (‘fast rejection’).
Performance• Detailed studies for all trigger types based on old simulations (basically results from 1998, only L2). • New studies to be done for HLT TDR (5/2003) with new HLT selection and L1 simulation SW.• Large uncertainties (physics+computing)
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AN ATLAS EVENT
H ZZ* e+e-+-
(mH = 130 GeV)
at high luminosity (1034 cm-2s-1)
The ‘hard’ Higgs event is overlaid with ~23‘minimum-bias’ and background events.
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Backup Material
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L1 SIMULATION: SUBSYSTEMSSimulation procedure; simplified view (only one storage instance).
RandomInputsData Files
Input zu HLT/DataFlow
ThresholdsTriggermenu
Hardware
Geant3 cells, test vectors
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menu tableof step N
HLT CONFIGURATION PRINCIPLE
Comps. CN-2
at step N-2
Signature SN
at step N
Signature SN-1
at step N-1Comps. CN-1
at step N-1
Signature SN-2
at step N-2
Comps. CN
at step NSignature sN
at step NComps. cN
at step N
Comps. cN-1
at step N-1Signature sN-1
at step N-1menu tableof step N-1
menu tableof step N-2
algo algo
algo
sequence table of step N
sequence table of step N-1
sequence table of step N-2
Recursive algorithms derives all ‘lower-level’ signatures (=intermediate decisions) using top-level (physics) signatures (XML definition) and set of implemented sequences (algorithms+in/outputs).
algo
algo
L1 RoIs
L1 RoIs
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HLT CONFIGURATION IMPLEMENTATION
Status
Well-tested software, used in many HLT applications. Currently: Development of ‘real-life’ algorithms which run on inputs of calo trigger simulation (HLT TDR!).
Code
Recursive algorithm implemented in C++ code in Athena framework (more complex than shown). Uses XML for definition of ‘Physics signatures und sequences. Embedded in HLT selection software (PESA steering code).
• One signature and one sequence
per step and ‘Physics Signatur’.
• One ‘Menu Table’ and one ‘Sequence Table’ per step.
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HLT: CONFIGURATION‘Top-down’ approach: • Input 1: Signature ‘2e30i’
• Input 2: all known sequences (Algos+In/Outputs)
List of all ‘PhysicsSignatures’ = Trigger Menu e30iAlgo-1e30
3: Then next-lower signature clear: 2-times e30: 2e30
1: ‘Physics Signature’
and constituents(2-times e30i) 2: Sequence:
Outputs,Algorithm,
Inputs
4: Procedure recursively down to2EM20i signature.One signature and one sequence per step.5: Signatures of all
‘Physics Signatures’in one step:
Menu Table
6: Sequences of all ‘Physics Signatures’
in one step:
Sequence Table