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Muons in ATLAS. Alexander Oh University of Manchester on behalf of the ATLAS Collaboration. ATL-COM-MUON-2010-024. Muons. Detector and Reconstruction Alignment and Calibration status Trigger Performance Reconstruction Performance. Detector: Muon Spectrometer. Fast trigger chambers: - PowerPoint PPT Presentation
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Muons in ATLASAlexander Oh
University of Manchesteron behalf of the ATLAS Collaboration
ATL-COM-MUON-2010-024
Alexander Oh (Manchester University) - ATLAS Collaboration 2
Muons
• Detector and Reconstruction• Alignment and Calibration status• Trigger Performance• Reconstruction Performance
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 3
Detector: Muon Spectrometer
4.10.2010
• Fast trigger chambers: – Resistive Plate Chambers (barrel)– Thin Gap Chambers (end-caps)
• Precision chambers:– Monitored Drift Tubes (barrel
and end-cap)– Cathode Strip Chambers
(forward region 2.0 < eta < 2.7)• Toroidal magnetic field of 0.5 T
– barrel and two end-cap toroids– 8 fold geometry– complex field
Alexander Oh (Manchester University) - ATLAS Collaboration 4
Detector: Inner Detector
4.10.2010
• Silicon Tracker– Pixels (3 layers)– Strips (4 barrel layers, 9 end-cap layers)– Coverage |eta| < 2.5
• Transition Radiation Tracker– Coverage |eta| < 2.0
• Solenoidal magnetic field of 2.0 T
Alexander Oh (Manchester University) - ATLAS Collaboration 5
Muon Reconstruction
• Muon Spectrometer Standalone (MS) reconstruction
• MS and Inner Detector (ID) combined fit– Outside-in– Inside-out– Statistical combination
• Taggers– ID track is matched to MS
segments– ID track is matched to a MIP in
calorimeter
4.10.2010
Objective: Muon identification in a wide momentum range from GeV (Onia) to TeV (BSM).Make use of all detector components and use different strategies:
Alexander Oh (Manchester University) - ATLAS Collaboration 6
Alignment and Calibration Status
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 7
Alignment and Calibration Status: MS
• Alignment– Optical alignment system
• Barrel: relative• End-caps: absolute
– Data with toroid B-field off.– Measure alignment with straight
tracks.
4.10.2010
Cosmics data 2008
barrel alignment±50 mm (large sectors)±100 mm (small sectors)
Cosmics data 2008
end-cap alignment±45 mm
Alexander Oh (Manchester University) - ATLAS Collaboration 8
Alignment and Calibration Status: ID
• Track based alignment– First alignment with cosmics tracks.– First collisions at 900 GeV were used
to improve the alignment.– Performance study with 7 GeV data.
New alignment constant set in progress.
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 9
Trigger Performance
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 10
Trigger• L1 custom hardware
– Require coincidence in eta phi view.– pT estimation based on geometrical
roads.– Road definition and time alignment
commissioned.
• HLT software– L2: Pattern recognition, LUT based pT
estimate – EF: Full muon reconstruction available
• L1, L2 and EF are commissioned and used for active rejection.
4.10.2010
see also Ricardo Goncalo: Atlas Trigger
TGC, timing optimization
Alexander Oh (Manchester University) - ATLAS Collaboration 11
Trigger• Efficiency determined by looking at
– Inclusive muons relative to offline. – Tag & Probe method on
J/Psi and Z events.• Trigger Efficiencies at L1
– barrel 75% – end-cap 95%
• Rel. Trigger efficiencies at HLT– L2 >98%– EF >98%
4.10.2010
L1 efficiency, T&P with J/PsiBarrel + End-caps
L1 efficiency, inclusive muonBarrel
EF efficiency, inclusive muonBarrel + End-caps
Alexander Oh (Manchester University) - ATLAS Collaboration 12
Trigger• Muon rates measured in data.• Extrapolation to higher luminosity.• Determines evolution of trigger strategy.
4.10.2010
Allocated rate
Alexander Oh (Manchester University) - ATLAS Collaboration 13
Reconstruction Performance
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 14
Reconstruction Efficiency• Determination from
Cosmics– Select events with ID
tracks traversing MS barrel.
– Look for MS track in • top hemisphere
(pID > 5 GeV) • bottom hemisphere
(pID > 9 GeV)
– Measures reconstruction efficiency of MS conditional to a L1 trigger.
4.10.2010
Turn on curve:Good agreement between Data and MC
Average efficiency:97.4 ±0.1 %95.2 ±0.1 %
ATLAS Preliminary2009 Cosmic Data
ATLAS Preliminary2009 Cosmic Data
Alexander Oh (Manchester University) - ATLAS Collaboration 15
Reconstruction Efficiency• Relative Efficiency from Data
– Use independent algorithms to assess reconstruction efficiency.
– Combined algorithm efficiency estimated by comparing overlap to calorimeter and segment tag algorithms.
– Tag and Confirm method with sample of J/Psi’s (purity ~98%)
– Tag and Probe studies are under preparation with J/Psi and Z.
4.10.2010
rel. eff. (%) data rel. eff. (%) MC
pT > 4 GeV 95.7±1.1 93.8±0.2
pT > 6 GeV 98.7±0.9 97.4±0.2
Alexander Oh (Manchester University) - ATLAS Collaboration 16
(Non-)Prompt Muons
Muons from light hadrons (“non-prompt”)•Decay within the ID volume• Hadron and the secondary muon are reconstructed
as one track•momentum mismatch of ID and MS pt
Muons from heavy flavour (“prompt”)•Secondary muon produced close to IP•ID and MS measure the muon track.
Discriminate by “loss momentum” fraction between MS and ID pT measurement:
Use templates derived from MC to determine fractions of “prompt” and “non-prompt” secondary muons.
4.10.2010
K0s -> p+p-J/Y -> m+m-
ID barrel
Alexander Oh (Manchester University) - ATLAS Collaboration 17
(Non-)Prompt Muons
• Fraction of prompt muons determined in bins of pT and eta.• MC and data agree within uncertainties• Dominant systematic uncertainties:
– template shape at low pT
– MC flavor content at high pT
4.10.2010
ID barrel
ID end-cap
Alexander Oh (Manchester University) - ATLAS Collaboration 18
Momentum Scale and Resolution• Use MS and ID pT
measurement to extract scale and resolution.
• Disentangle “prompt” and “non-prompt” contribution.– Background template
from QCD MC– Signal template: Gauss ×
Landau
4.10.2010
extract scale (xG) and resolution (sG+sL)
Alexander Oh (Manchester University) - ATLAS Collaboration 19
Momentum Scale and Resolution
4.10.2010
End-cap region:Due to alignment resolution in data worse then in MC.
Barrel region:Generally good agreement between data and MC.
Alexander Oh (Manchester University) - ATLAS Collaboration 20
Summary & Outlook• Performance of detector,
trigger and reconstruction studied with first data and cosmic events.
• Good agreement between data and MC.
• Presented results used only a fraction of the available data.
• Many more results to come soon with the full data set!
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 21
Backup
4.10.2010
Alexander Oh (Manchester University) - ATLAS Collaboration 22
Alignment and Calibration StatusMonitored Drift Tubes (MDT): Timing
• Constant time offset t0 for each channel.– Leading edge of drift
time spectrum.
• Radius – drift time relation (rt) determined from auto-calibration method– Adjusted using residual
distribution of track fit
• More statistics needed for final calibration– t0 from track segment
fitter– Resolution 20-50% worse
than optimal
4.10.2010
− t0 refit− RPC timing− testbeam
Alexander Oh (Manchester University) - ATLAS Collaboration 23
Fake Muons from pions
• Determine fraction of p being reconstructed as m.– decay-in-flight– punch-through
• High purity p sample from K0
s -> p+p-
– common vertex– transverse decay length [5 mm ,120 mm ]– p(p+p-) aligned with K0
s flight direction– Purity ~95%
• Probe: p ID track– p > 3 GeV– pT > 1 GeV
• Tag: Muon candidate associated to the p ID track.
4.10.2010
identified m
Alexander Oh (Manchester University) - ATLAS Collaboration 24
Fake Muons from pions• Fraction of fake muons extracted
by fit to K0s mass spectrum.
• Fake fraction – 0.101±0.014%
(combined and tagged)– 0.070±0.012% (combined only)
4.10.2010
• Good agreement between data and MC