ATLAS Muon Spectrometer

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ATLAS Muon Spectrometer
Dan Ventura UW EPE/PT Meeting 5/24/2006
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Spectrometer Layout
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Spectrometer Side View
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Chamber Types

• Precision Chambers
• Monitored Drift Tubes (MDT)
• Cathode Stripe Chambers (CSC)
• Trigger Chambers
• Resistive Plate Chambers (RPC)
• Thin Gap Chambers (TGC)
• CSC MDT RPC TGC
• Number of Chambers 32 1194 596 192
• Number of Channels 67000 370000 355000
  440000
• Area Coverage (m2) 27 5500 3650
  2900

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RPCs
Spacers
h
Read out
Graphite Film (High Voltage)
2 mm
Graphite Film (Ground)
f
Read out
Bakelite Slabs
Insulating Film

• 3 layers (2 on the BM MDTs, and 1 one the BO
  MDTs)
• 2 Gas gaps per Chamber
• Pick up plates segmented in 30-40 mm wide strips
• Spatial resolution of 1 cm for both coordinates
• Response time 1ns
• gt98 Efficiency

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Thin Gap Chambers

• Operating rates up to 20kHz/cm2
• 99 of arrival times lt 25 ns
• Azimuthal granularity 2-3 mrad
• Inner tracking layer has 2 layers of TGCs
• Provide azimuthal measurement
• Middle tracking plane has 7 layers of TGCs
• Provide azimuthal measurement, and trigger
  capabilities

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Triggering

• Low PT trigger
• Hits in 3 of the 4 inner tracking plane
• Hit in station 1 (station 1 for RPC, 3 for TGC)
  extrapolated to 2nd station along straight line
  through interaction point, look for hit in 2nd
  station within a coincidence window
• High PT trigger
• Logical AND of Low PT and at least hits in at
  least 1 of the 2 planes station 3 (RPC) or
  station 1 (TGC) are within coincidence window

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Cathode Strip Chambers
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CSCs (Contd)

• Located at hgt2 where count rate can be gt200
  Hz/cm2
• 2 track resolution for tracks separated in the
  bending direction by 5 mm
• Single Point Resolution (bending direction) 60
  mm
• Single Track Resolution (4 points in the bending
  direction) 40 mm
• Single Point Resolution (Azimuthal direction)
  0.5 cm

d S 2.54 mm Cathode Width 1.07 mm Inter Strip
Spacing .25 mm
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Monitored Drift Tubes

• Full Chamber consists of 2 multilayers of 3-4
  MDTs each

• Resolution with 6-8 hits 30 mm
• Chamber alignment is known to within 30 mm

30 mm
Single point resolution 80 mm
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Geometrical Acceptance
Superpoint a coincidence of at least 6 hits in
6 different layers of the MDT
Dashed 1 super point Solid 3 super
points Averaged over f
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Tracking

• COmBined Reconstruction for Atlas (COBRA)
• Has description of material and magnetic field as
  used by GEANT
• Allows for an accurate detector description while
  reconstructing tracks
• Tracks from the Muon System and Inner Detector
  are extrapolated to the inner surface of the
  Calorimeter, correcting for energy loss along the
  way
• Energy correction is made by using Calorimeter
  measurements (if isolated m) or by using material
  description
• c2 probability for track pairs to match is
  found
• After a successful match is found, a global fit
  is performed

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Toriodal B-field

• Large inter magnet spacing causes inhomogeneous
  B-field
• 5000 3D hall probes throughout the volume
• Largest gradients occur near the Barrel Inner
  Small (BIS) chamber
• DB .4 T

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References

• ATLAS TDR
• http//atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/TDR/
  TDR.html
• ATLAS Muon Spectrometer TDR
• http//atlas.web.cern.ch/Atlas/GROUPS/MUON/TDR/W
  eb/TDR_chapters.html
• Nikhef ATLAS Wiki
• http//www.nikhef.nl/pub/experiments/atlasw
  iki/index.php/Chapter_II
• Salamon, Andrea. The RPC first level muon trigger
  in the barrel of the ATLAS experiment, 2005.
  Talk given at VIII Workshop on Resistive Plate
  Chambers and Related Detectors
• Valderanis, Ch. r(t) dependence on magnetic
  field First results, 2004. Talk given at
  Test-Beam and Alignment meeting