Post on 24-Feb-2016
description
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Rosemarie AbenSupervisor: Peter Kluit
Track: Particle and Astroparticle Physics
Muon-raying the ATLAS Detector
Amsterdam Master of Physics Symposium, 16 April 2010
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Outline
• LHC and ATLAS• The muon spectrometer of ATLAS• Precision measurements• Sagitta Analysis• Sagitta Resolutions• ATLAS Now
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Standard Model & Higgs
?Solution:
Energy per Collision 14 TeV
Protons per bunch 1011
Bunches per ring 2835
Design Luminosity 1034 cm-2 s-1
Circumference 27 Km
Collisions per bunch 25
Detection of Higgs decay:H ZZ 4µ “Golden Channel”
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Exotic physics and ATLAS
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Layout of the Muon spectrometer• Trigger chambers: trigger on muons• Precision chambers: Reconstruction of muon
tracks
Small and Large muon stations
Three layers of muon stations
Sector, containing 12
Measurement towers
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Monitored Drift Tube (MDT) Chambers
Tube diameter 30 mm
Diameter Sense wire 50 μm
# Tubes per chamber Up to 432
Length MDTs 1-6 m
# MDT chambers 1150
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Precision Measurements and SagittaNeeded accuracy MDT chamber: 10% for 1 TeV muons Knowledge about the precision of the chambers is extremely important.
Contributions to precision: alignment and calibration.
Reconstructed Track Sagitta Misalignment
Sagitta: measure for the precision of the MDT chambers.
Outer
Middle
Inner
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Sagitta DistributionDistribution of the sagittas for all barrel sectors.
Sagitta [mm]
# Tr
acks
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Sagitta Distribution Improvements
Misalignment was seen in certain towers: shifts and extra peaks.
With this knowledge improvements have been made.
New analysis shows good alignment!
Old alignment Improved alignment
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Sagitta Resolution FitResolution: necessary to monitor the performance of the muon chambers in measuring momentum and position.Sagitta resolution is a measure for the accuracy of the chambers depending on alignment + calibration + chamber geometry + chamber deformations+ ...
Each slice is fitted with a double Gauss fit and the standard deviation of the smaller Gauss is taken to do the final fit, using:
σ (sagitta) = √( P1² + P2²/momentum²) • P1 = intrinsic resolution term: gives the sagitta resolution• P2 = multiple scattering term
10-20 GeV 20-40 GeV 40-70 GeV 70-110 GeVSlices up to 350 GeV.
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Sagitta Resolution from Cosmic Data
Large sectors
Sagitta resolution: 101 ± 6 μm
Intrinsic termMultiple Scattering term
Sagitta resolution: 143 ± 16 μm
Small sectors
Last November the sagitta resolutions were still around 200 μm….
But, is this as expected?
Look to simulated cosmic muons!
Latest results
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Sagitta Resolution from Simulated Cosmics
Sagitta resolution: 63 ± 2 μm
Large sectors
Sagitta resolution: 102 ± 5 μm
Small sectorsSimulation
Comparison with data: 101 μm for Large sectors and 153 μm for Small sectors. Difference between data and simulation due to effects not yet corrected for.
But accuracy is already good enough for the muons coming from latest collisions.Muons ready to be reconstructed in ATLAS!
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Time for questions.
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Summary and Conclusions
• The sagitta is a good measure to study the achieved precision of the MDT chambers with respect to alignment and calibration;
• The sagitta resolution is a measure for the accuracy of the chambers;• Sagitta resolution:
- Resolutions for large sectors, data vs. MC: 101 μm vs. 63 μm.
- Resolutions for small sectors, data vs. MC: 143 μm vs. 102 μm.
The MDT chambers are ready for analysis of the 7 TeV Data!!!
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