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ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 1
ATLAS Detector Status & PerformanceH. H. Williams (University of Pennsylvania)Representing the ATLAS Collaboration
pT (j1)=420 GeVpT (j2)=320 GeV
Highest-mass di-jetevent observed so far:Mjj = 2.55 TeV
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 2
Inner Detector (|η|<2.5, B=2T): Si Pixels, Si strips, Transition Radiation detector (straws) Precise tracking and vertexing,e/π separationMomentum resolution: σ/pT ~ 3.8x10-4 pT (GeV) ⊕ 0.015
Length : ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons~108 electronic channels3000 km of cables
Muon Spectrometer (|η|<2.7) : air-core toroids with gas-based muon chambersMuon trigger and measurement with momentum resolution < 10% up to Eμ ~ 1 TeV
EM calorimeter: Pb-LAr Accordione/γ trigger, identification and measurementE-resolution: σ/E ~ 10%/√E
HAD calorimetry (|η|<5): segmentation, hermeticityFe/scintillator Tiles (central), Cu/W-LAr (fwd)Trigger and measurement of jets and missing ETE-resolution: σ/E ~ 50%/√E ⊕ 0.03
3-level triggerreducing the ratefrom 40 MHz to~200 Hz
The ATLAS Detector
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Operational Efficiency
Pixel
SCT
TRT
100% channels operational97%
95% data-taking efficiency
Fraction of data labeled “Good” by subsystem
Fraction of Channels Operational by subsystem
Integrated Luminosity
(Efficiency includes time to ramp pixel, silicon bias voltage after stable beams declared)
Luminosity detectors calibratedwith van der Meer scans. Luminosity known today to ~11% (error dominated by knowledge of beam currents)
LArEMCalor
TileCalor
EndCLArCalor
ForwLArCalor
LVL1CaloTrig
LVL1MuonRPCTrig LVL1
MuonTGCTrig
MuonDriftTube
MuonCSC
RPCDet.
TGCDet.
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 4
Trigger commissioning and operation3 levels: LVL1, LVL2, Event Filter (EF) High-Level-Trigger (HLT) : LVL2 and EF
Un-prescaled rates of some LVL1 items vs L
HLT on (e/γ) for EM2, EM3J5 pre-scaled
HLT on (τ)for TAU5
HLT on (μ) for MU0 fwd
300 Hz
Trigger output: typically 300 HzHistory:
L < few 10 27 cm-2 s-1: minimum-bias LVL1 trigger: hits in scintillatorcounters (MBTS) located at Z=± 3.5 m from collision centreL > 1027 cm-2 s-1 : MBTS prescaled(only fraction of events recorded)0thers items (EM2, J5, TAU5, MU0..): un-prescaled
L ~ 1029 cm-2 s-1: start to activate HLTchains to cope with increasing ratewhile running with low LVL1 thresholds.Jet items: prescaled (HLT rejection small)Figure gives examples for L up 7x1029
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 5
Tracking efficiency at HLT for electron candidates with ET
off (calo) > 5 GeV
Crucial for J/ψ ee
LVL1 jet trigger efficiency for the lowest threshold (J5)
Crucial for jet cross-section
LVL1 forward muon trigger efficiencyfor the lowest threshold (MU0)
Crucial for di-muon resonances
Example of trigger performance studies
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
ATLAS Inner Detector Tracking
η < 2.5Immersed in 2 Tesla fieldIntrinsic Position Resolution10μ pixels, 17μ SCT, ~130μ TRT in R,φ115μ pixels, 580μ SCT in z (barrel)
Pixels3 barrel layers, 3 disks each endcap1744 modules
Silicon Strip Detectors (SCT)4 barrel double-sided, 9 disks in endcaps4088 modules
Transition Radiation Tracker (TRT)4 mm straw proportional drift tubesTracking and transition radiation detection298k straws
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Pixel Detector - Highlights
• Electronics measures time-over-threshold (Tot)
• Tot ~ charge deposition ~ dE/dx• dE/dx depends on β • 3 pixel hits allows good dE/dx
measurement
Deuterium
Protons
Kaons
Pions
Neg trks Pos trks
σdata~ 25μ
Particle ID via dE/dxPosition Residuals
(Really FWHM/2.35)
φ -> K+K-
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Silicon Strip Detector (SCT) - HighlightsSCT Efficiency SCT Residuals
Lorentz Angle – Measured & Modeled
σdata~ 42μ
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Transition Radiation Tracker (TRT) - HighlightsMeasures Drift Time and Trans. Rad. Photons Track Position vs Drift Time (R-t)
Position Residuals in TRT Barrel
σdata~ 141μ
Electron ID using Number TR Photons
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Combination of Pixel/SCT & TRT Very Powerful
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 11
Impact Parameters & Secondary Vertices
Impact Parameter – d0
Decay Length Significance – L/σ
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams~ 10-45 tracks with pT >150 MeV per vertexVertex z-positions : −3.2, −2.3, 0.5, 1.9 cm (vertex resolution better than ~200 μm)
Event with 4 pp interactions in the same bunch-crossing
Multiple Primary Vertices
Already at 1.6 * 1030 mean number interactions~ 1.3
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 13
Λπ-
π-
p
PDG: 1321.32Ξ Λπ
Tracking: from early observation of peaks to cascade decays and J/ψ ee
78 nb-1
J/ψ e+e- Momentum scale known to permil in this rangeResolution as expected (multiple scattering)Complex algorithms (cascades, b-tag, Bremrecovery, …) work wellWorking on material, alignment, data-driven efficiencies, …
- Ks π+π-
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 14
J/ψ provides large samples of low-pT muonsto study μ trigger and identification efficiency, resolution and absolute momentum scale in the few GeV range
Absolute momentum scale known to ~ 0.2% and momentum resolution to ~2 % in the few GeV region
J/ψ mass peak vs muon η J/ψ mass resolution vs muon η
PDG
5 MeV
Inner DetectorInner Detector
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 15
Mapping the Inner Detector materialwith γ e+e- conversions …
Data
Beam
pip
e Pixe
l 1
Pixe
l 2
Pixel 3
SCT 1SCT 2
√s = 7 TeV
Pixel supportstructures
π0 Dalitzdecays
Reconstructed conversion radiusof γ e+e- from minimum bias
Data show that Pixel supports are displaced in the simulation
Reconstruction of Conversions: γ e+e-
Reconstruction of Conversions veryimportant for Higgs -> γγ and manyOther physics processes
Charged particle interactionsalso being used succesfully.
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
The ATLAS calorimeter system (1)
Liquid Argon (LAr) detectors in 3 cryostats |η|<5
17m
4m 9m
Surrounded by Tile Calorimeter |η|<1.7
Intrinsically linear and stable with timeIntrinsic radiation-hardExcellent time resolution
Maximum absorption depth at least cost
1780
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
The ATLAS calorimeter system (2)
Sampling EM calorimeterAbsorber : lead with accordion shapeActive material : liquid argon (90 K)
Readout : large electrodes (2 m2)
S1 : ΔηxΔφ ~ 0.003x0.1
S2 : ΔηxΔφ = 0.025x0.025
γ/π0 separation
Shower develops
Shower ends
PS : ΔηxΔφ ~ 0.025x0.1Recover energy loss
Sampling hadronic calorimetersMix of technologies to cover |η|<5
Steel + Tile scintillators TileCopper + LAr HECCopper/Tungstate + LAr FCal
Hermetic in φ, very granular (173k cells)Good e(γ) resolution, e/jet separation
S3 : ΔηxΔφ = 0.05x0.025
Hermetic (>10 λ) up to |η|<5Good jet and Etmiss resolution
10λ
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Performance of EM Calorimeter Extract prompt electron/γ samples using EM calorimeter granularity
Good data-MC agreement for ATLAS EM calorimeter identification variables
S3
S2
S1PS
γ π0Electron vs hadrons
(E±3−E±1)/E±1
E(S1)/Etot
Relative energy outside S1
shower core
ET(cluster)>7 GeV, |η|<2.0, track, EM-like shower in S2
ET>10 GeV, loose identification
>2
16
~4
X0 Layer
(E±3−E±1)/E±1
Photons vs π0
Fraction total energy in S1
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 19
Number of clusters in jets pT>7 GeVvs number of tracks
Longitudinal jet profile
Jet radial shape
E(calorimeter)p(tracker)
vs p
Isolated hadrons
E
+5%-5%
Properties of Jets and Calorimeter Response
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 20
Jet Energy Scale uncertainty
Jet momenta corrected (for calorimeter non-compensation, material, etc.) usingη/pT-dependent calibration factors derived from MC (need ~ 1 pb-1 for in-situ γj)
Today JES known in ATLAS to : ~ 7%
Dominant uncertainty on jet cross-section measurement Ultimate goal: ~1%
Builds on detailed foundation work tounderstand main ingredients by comparing MC/data (see before)Many sources of systematic uncertainties studied in detail
pTprobe
pTref (| η |< 0.8)
Inter-calibration central-forward checked using jet pT-balance
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Missing transverse energy
Calibrated
Measured over ~ full calorimeter coverage (3600 in φ, |η| < 4.5, ~ 200k cells)
Sensitive to calorimeter performance (noise, coherent noise, dead cells, mis-calibrations, cracks, etc.), and cosmics and beam-related backgrounds
ETmiss spectrum from SUSY searches:
events with ≥ 3 high-pT jets
SUSYx10
Calibrated ETmiss from
minimum-bias events
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 22
Observed event with hardest jet
Event display shows uncalibrated energies
pT (j1)= 1120 GeVpT (j2)= 480 GeVpT (j3)= 155 GeVpT (j4)= 95 GeV
pT (jet) > 1.12 TeV
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Atlas Muon System
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
As seen by a W -> μ ν event
Efficiency
Chamber Resolution
σcore ∼ 100μAlignment
σ ~ 430μ
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams
Muon System Momentum Resolution
Data (cosmics) Data (cosmics)
MC (cosmics)MC (cosmics)
Large Muon Sectors Small Muon Sectors
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 26
Simple analysis:LVL1 muon trigger with pT ~ 6 GeV threshold2 opposite-sign muonsreconstructed by combining tracker and muon spectrometer both muons with |z|<1 cm from primary vertex
Looser selection: includes also muons made of Inner Detector tracks + Muon Spectrometer segmentsDistances between resonances fixed to PDG values; Y(2S), Y(3S) resolutions fixed to Y(1S) resolution
Full data sampleDi-muon resonances
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 27
Z ee, μμ measurements σ NNLO (γ*/Z ll) ~ 0.99 nb per family for M(ll) > 60 GeV
GeV ee μμPeak 89.6± 0.8 90.5 ± 0.8Width (ΓZ unfolded) 3.6 ± 0.8 4.2 ± 0.8
From the sub-sample (~ 225 nb-1) used for the cross-section measurement
still some work to do on alignment of ID and forward muon chambers, and oncalorimeter inter-calibration, to achieve expected resolution
ATLAS status LBNL-MIT LHC Workshop 10-13 August, 2010 H. H. Williams 28
Observed in data W eν (296 nb-1): 815 events W μν (291 nb-1): 1111 events
W eν: 815 events
W μν: 1111 events
Work to determine systematic uncertainties(ET
miss, …) in the presence of pile-up ongoing W cross-section and asymmetry measurements
presented here are based on first 17 nb-1 (recorded at lower instantaneous luminosity)
After call cuts except mT
After all selections
Full data sample