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Sez. di Lecce
Universita` degli Studi del Salento
The Muon Trigger in ATLAS
Giovanni SiragusaOn behalf of the ATLAS Muon Trigger group
2007 April 24 Giovanni Siragusa - ACAT 2007
2
Outline• The LHC and Trigger system requirements• The ATLAS detector:
– The Muon Spectrometer– The Trigger System
• Muon Trigger System architecture and performance:
– Level 1– Level 2– Event Filter
• Trigger Commissioning• Conclusions
2007 April 24 Giovanni Siragusa - ACAT 2007
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LHCCenter of Mass Energy:– 14 TeV (p-p)
Design Luminosity:– L = 1034 cm-2s-1
Integrated Luminosity per year (@ 1034) Ldt 100 fb-1
The cross sections of interesting physics processes are highly suppressed w.r.t. tot
– Calibrations and precision physics
• Leptonic W decay– New Physics
• Higgs boson production
10-6
10-9
Event rate at LHC (@ design lumi) is ~1 GHz– 40 MHz (BC frequency) x 23 interactions per BC
Maximum allowed acquisition rate is ~200 Hz– Bandwidth ~ 300 MByte/s
– Event Size ~ 1.5 MByte Trigger with high
rejection capability
Trigger with high
selection efficiency
2007 April 24 Giovanni Siragusa - ACAT 2007
4 The ATLAS detector
General purpose detector
– Capability to observe a wide range of Physics processes
Study of the Physics of the Standard Model and beyond it
– SUSY, Extra Dimensions
– Any exotic scenario of new Physics at TeV energy scale
First collisions for physics in 2008
Now commissioning detector and trigger with cosmic rays
Inner Detector:
– Silicon detectors: pixel, micro-strips
– TRT
– Thin superconducting magnet with a solenoidal field of 2T
Electro Magnetic Calorimeter
– Sampling Pb - Argon
(liquid @ 80K)
Hadronic Calorimeter
– Scintillation tiles
Muon Spectrometer (MS)
– Toroidal magnetic field in air (bending in the z- plane
– High resolution
(e.g. ~50 m sagitta)
Physics
Design
2007 April 24 Giovanni Siragusa - ACAT 2007
5The ATLAS Muon Spectrometer
CSCCSC
RPCRPC
TGCTGCMDTMDT
Design resolution on the sagitta measurement:
50 m
10% of relative resolution for muons with
pT ~ 1 TeV
•High-pT muons are an important signature for many known (and predicted) processes at TeV energy scale•Low-pT muons are the major source of Level1 trigger rate
Muons loose in the calorimetric system ~3GeVMuons with pT above 3 GeV arrive at the MS
1. Precise measurements of high pT muons
2. Identification of low pT muons
Inhomogeneous toroidal magnetic field in air
1. Max field 4T2. Multiple
scattering
suppression
2007 April 24 Giovanni Siragusa - ACAT 2007
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~100 kHz
~2 kHz
~200 Hz
2.5 s
10 ms
2 s
The ATLAS Trigger systemLevel 1 (hardware)•Coarse granularity data from CALO and MUON detectors•Selects Regions Of Interest (ROI) in the detector
Level 2 (software)•Algorithms optimized for fast rejection•It accesses full granularity data, only inside ROIs
Event Filter (software)•Uses the Offline algorithms•It can access data from the entire event (after the Event builder)•Seeding strategy
Reduced bandwidth at Level 2 input
Full event access
2007 April 24 Giovanni Siragusa - ACAT 2007
7 The ATLAS Muon Trigger
FasFastt
B Physics processor
TileTile
CombComb
TrigDiMuoTrigDiMuonn
IsolIsolComCombb
10 ms latency time
TrigMooreTrigMoore
MOOREMOORE
2 s latency time
Level 1Level 1 SimulationSimulation
capability to run on the HLT farms to optimize the
hardware selection
Level 2 SelectionLevel 2 Selection EF SelectionEF Selection
RPCRPC
TGCTGC
CTPICTPI CTPCTP
2.5 s latency time
MuId SAMuId SA
MuId COMBMuId COMB
MSMS
CALOCALO
IDID
H i g h L e v e l T r i g g e r
High-pT physics
Low-pT physics
2007 April 24 Giovanni Siragusa - ACAT 2007
8 Level 1 selection
The selection is based on the definition of allowed geometrical roads, the
Coincidence Windows, whose center is defined by the infinite momentum track
The width of the road defines a pT threshold
ToroidToroidToroidToroid
Three pT thresholds can be applied for a Level 1 configuration
• 6, 8, 10 GeV (Low-pT)• 11, 20, 40 GeV (High-pT)
The Coincidence Window is implemented with FPGA
Can be reconfigured to optimize the algorithm for different running conditions
2007 April 24 Giovanni Siragusa - ACAT 2007
9Level 1: Acceptance
~30% of barrel inefficiencies are due to feet and elevator sectors
3-station coincidencetrigger efficiency of TGC
Endcap6 GeV20 GeV
Level 1 barrel acceptance:Level 1 barrel acceptance:•83%83% Low-p Low-pTT
•79%79% High-p High-pTT
Level 1 simulation results
Barrel Low pT OK, NO High pT
NO Trigger
single muons, pT 100 GeV
2007 April 24 Giovanni Siragusa - ACAT 2007
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pT
Level 1: Efficiency curves
1. The value at the plateau is due to the acceptance
2. The sharpness of the ramp-up is a function of the resolution
3. The efficiency above the threshold is due to fake tracks impact on the trigger rates
•6 GeV
•8 GeV
•10 GeV
Low-pT thresholds
•11 GeV
•20 GeV
•40 GeV
High-pT thresholds
Level 1 simulation
6 GeV20 GeV
Endcap
0.4
0.8
Barrel
2007 April 24 Giovanni Siragusa - ACAT 2007
11 Level 1: Rates
Ri Ld i
dpTpT _ inf
pT _cutoff
(pT ) dpT
Inclusive μ cross-section @ LHC
(prompt μ and /K decay)
•6 GeV
•8 GeV
•10 GeV
Level 1 efficiency
Level 1 simulation
threshold [GeV]
Rat
e [H
z]
Expected single muon trigger rates at a luminosity of 1033 cm-2s-1
The cosmic configuration is showed as an effective threshold of 3 GeV
Barrel only
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FastConfirm the Level-1 trigger with a
more precise pT estimation within a “Region of interest (RoI)”
Contribute to the global Level-2 decision.
“Global Pattern Recognition” involving trigger chambers and positions of MDT tubes (no use of drift time)
“Track fit” involving drift time measurements, performed for each MDT chamber
Fast “pT estimate” via a Look-up-table (LUT) with no use of time consuming fit methods
Refine the Fast pT using ID data
– more sharpness @ 6 GeV threshold
Identify the muon track in ID to ease the search for secondary muon tracks.
High reduction on the /K was obtained thanks to the pT match
Comb
Level 2
Isol uses calorimetric information to select isolated muons from W and Z decays
Tile identifies low pT muons using the measure of the energy loss in the calorimeters
Threshold Fast - Hypo Comb - Hypo
Low-pT
(6 GeV)
99.5 – 98.5
(10 GeV single )
96.3 – 96.1
(10 GeV single )
High-pT
(20 GeV)
99.6 – 96.7
(50 GeV single )
95.0 – 94.8
(50 GeV single )
Efficiencies
2007 April 24 Giovanni Siragusa - ACAT 2007
13 Level 2: Resolution
Barrel
End Cap
Fas
t
Comb
idScan
50 GeV 10 GeV 5 GeV
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Event FilterThe Muon Event Filter
(TrigMoore) uses the same Algorithms as the Offline.
The Feature Extraction Algorithms (FEX) calculate the muon track parameters
Operating configurations:
– Seeded from Level 2 (Standard)
– Seeded from Level1 (Trigger studies)
– Unseeded (Full Event Reconstruction)
The Trigger Decision operates via the insertion (in any point of the trigger chain) of the Hypothesis Algorithms (Hypo)
MooAlgsMooMakeRoadsMooMakeTracks…
MooStatistics
MooEvent
TrigMoore
MooHLTAlg
MuonIdentification
Hypo and FEX define a trigger sequenceEvents are selected if they satisfy an item in the trigger menu
Offline
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TrigMooreMOORE
– Reconstruction of the tracks in the Muon Spectrometer (MS)
Muid Stand Alone– Propagation of the tracks to the
Impact Point(using calorimetric measurement)
– Good pT resolution (less than 10% at 1 TeV)
Muid Combined– Combines the MS tracks with
Inner Detector (ID) tracks– Refines pT resolution
• ID improves resolution at low pT (less than 50 GeV)
• MS improves resolution at high pT
Moore AlgsMoore Algs
MuIdStandAloneMuIdStandAloneAlgs Algs
Seeding AlgsSeeding Algs
MuIdCombinedMuIdCombinedAlgs Algs
HypoHypo
HypoHypo
HypoHypo
CALOCALO
IDID
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< 2.5
pT resolutions
100505
Single muonsTrigMoore: Resolution
The low amount of material in the Muon Spectrometer reduces the multiple scattering
The resolution performances are highly related to the chambers alignment
Single muons pT resolution is under 4%(for pT < 100 GeV)
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Inefficiencies in the feet region
40 GeV muons selection efficiency
40 GeV muons selection efficiency
Barrel – End Cap transition
TrigMoore: EfficiencyEfficiency is defined with respect to the seeding level
Here the efficiency is referred to Level 2 (standard configuration)
High efficiency (95%) for muons up to 1 TeV transverse momentum
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EF: Rates
10 33 cm -2s -1
At low pT the single muon rate is dominated by /K decays in flight
Muon sources6 GeV/c threshold
kHz/K/K 1.9
BB 0.67
CC 0.34
WW 0.003
TT negligible
TotalTotal 3.0 kHz3.0 kHz
Barrelmu(6) 3.0 kHzmu(20) 25 Hz
End-Capmu(6) 3.1 kHzmu(20) 27 Hz
Total (@ 1033 cm-2s-1):
mu(6) 6.1 kHz mu(20) 52 Hz
Bar
rel o
nly
2007 April 24 Giovanni Siragusa - ACAT 2007
19 Cavern backgroundThe p-p collisions generate a radiation that
interacts with the detector’s and accelerator’s materials
As a consequence neutral and charged particles are released(photons and neutrons)
– particles diffuse like a gas in the cavern, giving rise to time uncorrelated hits (fake tracks)
– This effect increases linearly with luminosity
Safety Factor (SF) = a factor that multiplies nominal background – it takes care of possible underestimations of the background
Co
un
tin
g r
ate
s (
kH
z/c
m2)10-1
10-2
10-3
Background from neutral and charged
L=1034cm-2s-1
Outer Station
Inner Station
Middle Station
Fake track prob. on single muon, SF=x5Fake track prob. on single muon events
x10
x5x2
no
No pT threshold applied !
Geant3Geant4
2007 April 24 Giovanni Siragusa - ACAT 2007
20 Trigger on complex events
The muon trigger selection has been performed on complex events (top events are shown)
Realistic simulation of trigger is included in Physics Analysis
Started the Monitoring and Data Quality activity to be ready for real data taking
Muons absorbed in Calorimeters
Feet region
Crack
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Misaligned Geometry
Comparison of the resolutions of the EF algorithms for nominal and “real” geometry (material distortions, inhomogeneous magnetic field)
The Computing System Commissioning will be based on simulated data that will reproduce in the maximum detail real data
nominal-nominal misal-misal
• Blue = MOORE• Red = MuidSA• Magenta= MuidCB
misal-nominal
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Trigger Commissioning:Run in February 2007 with cosmics data
Trigger (Level 1 + HLT) run OnlineUnfortunately MDT chambers off. Tested HLT workflow and architecture
RPC Chambers of Sector 13 provided cosmic-ray trigger signalFull hardware Central Trigger Processing chain in placeFull hardware and software for Level 2 handling (processors, readout links, HLT sw suite)Version of the Level 2 algorithm optimized for cosmic rays identification has been successfully running and triggering
First Cosmic Run
Efficiency (plateau)
pT @ 90%
83.3% 3.5 GeV
x
y
Sector 13
UX15
Reconstructed Muon Eta
Reconstructed Muon Phi
Level 2 – RPC only
Level 1 cosmic setting:opening the concidence windows as much as possible
•minimum Level1 threshold value is limited by RPC cabling
Level 1
simulation
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Conclusions
• Next year we will have first collisions at LHC
• First test on cosmic data have been performed and all the systems are extensively checked and tested
• All the studies on the muon trigger indicate that the major requirements are satisfied
• Optimization of the trigger chain will be possible in the first stages of LHC operation (low luminosity)
• The ATLAS trigger system will be ready for Physics and data taking
2007 April 24 Giovanni Siragusa - ACAT 2007
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Backup
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LVL1 barrel: Cosmic setting
pT [GeV]
Cosmic setting is obtained by opening the concidence windows as much as possible, minimum lvl1 threshold value is limited by RPC connectivity. It have been used for Sector 13 data taking and for the future trigger commissioning
Level 1 simulation
2007 April 24 Giovanni Siragusa - ACAT 2007
26LVL1 barrel : Low-pT Trigger rates
Using the Level-1 Efficiency curves we may
estimate the rates with different threshold.
Muon sources
10 GeV10 GeV threshold
Lumi=1033
8 GeV8 GeV threshold
Lumi=1033
6 GeV6 GeV threshold
Lumi=1033
5 GeV5 GeV threshold
Lumi=1033
"Cosmic""Cosmic"thresholdLumi=1033
/K 5400 Hz 8830 Hz 10470 Hz 21800 Hz 62500 Hz
b 920 Hz 1160 Hz 1650 Hz 2220 Hz 3360 Hz
c 510 Hz 660 Hz 970 Hz 1400 Hz 2400 Hz
W 3 Hz 3 Hz 3 Hz 3 Hz 3 Hz
t Negligible Negligible Negligible Negligible Negligible
Sum 6.8 kHz 11 kHz 13 kHz 25.5 kHz 68.3 kHz
Level 1 simulation
2007 April 24 Giovanni Siragusa - ACAT 2007
27 Level 1 barrel :High-pT Trigger rates
Muon sources
11 11 GeVGeV threshold
Lumi=1034
2020 GeV GeV threshold
Lumi=1034
/K 7420 Hz 3540 Hz
b 2330 Hz 760 Hz
c 1100 Hz 340 Hz
W 28 Hz 26 Hz
t Negligible Negligible
Sum 12 kHz 4.7 kHz
Preliminary
Level 1 simulation
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Level 1 endcap: Rates
Muon Sources
6 GeV6 GeVthreshold
Lumi=1033
/K 5.9
b 1.8
c 1.0
W negligible
t negligible
Sum 8.7 KHz
20 GeV20 GeV thresholdLumi=1034
40 GeV40 GeV thresholdLumi=1034
6.9 3.60
1.3 0.48
0.7 0.27
0.04 0.04
negligible negligible
8.9 KHz 4.4 KHz
Level 1 simulation
2007 April 24 Giovanni Siragusa - ACAT 2007
29 Level 2: Efficiency
GeVFast
eff.
6
GeV
Comb
eff.
6
GeV
Fast
eff.20
GeVComb
eff.
20
GeV
5 98.2% 20.5% 18.7% 0.2% ---- ---- ---- ----
10 99.5% 98.5% 96.3% 96.1% 99.5% 3.3% 3.2% < 0.1%
50 99.6% 98.8% 97% 97% 99.6% 96.7% 95.0% 94.8%
100 99.6% 98.5% 96.7% 96.7% 99.6% 96.5% 94.9% 94.9%
300 98.8% 98.1% 94.9% 94.9% 98.8% 94.2% 92.6% 92.6%
Low - pT High - pT
Hypo off Hypo on
The Efficiency is shown for FEX algorithm and after the HYPOTHESIS algorithm cut