Installation of the first of the big wheels of the ATLAS muon spectrometer, a thin gap chamber (TGC) wheel
The muon spectrometer will include four big moving wheels at each end, each measuring 25 metres in diameter. Of the eight wheels in total, six will be composed of thin gap chambers for the muon trigger system and the other two will consist of monitored drift tubes (MDTs) to measure the position of the muons (Image: CERN)

Muon Spectrometer

Identifies and measures the momenta of muons

Muons are particles that usually pass through the Inner Detector and Calorimeter undetected. The muon spectrometer, made up of 4,000 individual muon chambers using four different technologies by 48 institutions in 23 production sites around the world.

Subsections of the Muon System: Thin Gap Chambers, Resistive Plate Chambers, Monitored Drift Tubes, and Cathode Strip Chambers.

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Thin Gap Chambers

Thin Gap Chambers

  • For triggering and 2nd coordinate measurement (non-bending direction) at ends of detector.
  • 440,000 channels
Resistive Plate Chambers

Resistive Plate Chambers

  • For triggering and 2nd coordinate measurement in central region.
  • 380,000 channels
  • Electric Field 5,000 V/mm
Monitored Drift Tubes

Monitored Drift Tubes

  • Measure curves of tracks.
  • 1,171 chambers with total 354,240 tubes (3 cm diameter, 0.85-6.5 m long).
  • Tube resolution 80 μm
Cathode Strip Chambers

Cathode Strip Chambers

  • Measure precision coordinates at ends of detector.
  • 70,000 channels
  • Resolution 60 μm
This colorful 3D animation is an excerpt from the film "ATLAS-Episode II, The Particles Strike Back." Shot with a bug's eye view of the inside of the detector. The viewer is shown the design of the Muon Spectrometer, what happens when particles pass through it and what it measures. (Video: CERN)