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TRIGGERING IN THE ATLAS
EXPERIMENT
Thomas Schörner-SadeniusUHH
Teilchenphysik II4. November 2005
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 2
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!
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 3
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.
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 4
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 5
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 6
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-SamplerAgainst effects of
energy losses in front of calorimeters
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 7
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 8
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 9
THE LEVEL1-TRIGGERSelection based on high-pT objects from calo and muon.
MultiplicitiesRegions-
of-InterestEvent decision
for 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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 10
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.
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 11
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 chambersprecision chambers
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 12
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 13
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!)
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 14
THE HIGH-LEVEL TRIGGER (HLT)Good example for solid software process.
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 15
HLT: DESIGN OVERVIEW
EventFilter (EF)
ClassificationSelection~102 Hz
Hardware Implementation
LEVEL 2 (LVL2)~1 kHz
Level1 (L1)
~102 kHz
Read-OutSubsystemModules
High-Level Trigger: Design
HIGH-LEVEL TRIGGER (HLT)
Offline
Simplified subsystem view
Event- Filter
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 16
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>>
InterfaceDependency
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 17
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
Teilchen 2, 4. November 2005 TSS: Triggering in ATLAS 18
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.