This model has now been moved here.

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The Compact Muon Solenoid (CMS) detector is one of the big four experiments of the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator. The LHC is part of CERN's accelerator complex in Geneva, Switzerland. The detector is located 100 meters underground near Cessy, France, at the opposite end of the LHC from ATLAS detector. It is 15 meters high and 21 meters long, and it weighs 14,000 tonnes.

This 120:1 scale model shows CMS' most important components. It is based on the original Technical Design Reports and the SketchUpCMS project. It was originally modeled by James Wetzel, W.G. Wetzel and Nick Arevalo with a grant from Don Lincoln. Some parts have been modified by me for ease-of-printing or cosmetics.

Objective of CMS

CMS is a general-purpose detector with a broad physics programme ranging from studying the Standard Model (including the Higgs boson) to searching for extra dimensions and particles that could make up dark matter.

Components

The CMS detector is shaped like a cylindrical onion, with several concentric layers of components. These components help prepare “photographs” of each collision event by determining the properties of the particles produced in that particular collision.

Particle collisions occur at the very center of the detector, within the LHC accelerator's beam pipes. Inside the accelerator, two high-energy particle beams travel at close to the speed of light before they are made to collide. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field maintained by superconducting electromagnets.

The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 tesla, about 100,000 times the magnetic field of the Earth. The field is confined by a steel “yoke” that forms the bulk of the detector’s 14,000-tonne weight.

CMS acts as a giant, high-speed camera, taking 3D “photographs” of particle collisions from all directions up to 40 million times each second. Although most of the particles produced in the collisions are “unstable”, they transform rapidly into stable particles that can be detected by CMS. By identifying (nearly) all the stable particles produced in each collision, measuring their momenta and energies, and then piecing together the information of all these particles like putting together the pieces of a puzzle, the detector can recreate an “image” of the collision for further analysis.

Here is a brief description of each component represented in the model, as seen from the inside out:

• Barrel_6_Tracker.stl
  The Silicone Tracker is made of around 75 million individual electronic sensors arranged in concentric layers. When a charged particle flies through the Tracker layer, it interacts electromagnetically with the silicon and produces a hit -- these individual hits can then be joined together to identify the track of the traversing particle.
• Barrel_5_ECAL.stl
  The Electromagnetic Calorimeter (ECAL) measures the energy of electrons and photons by stopping them completely.
• Barrel_4_HCAL.stl
  The Hadron Calorimeter (HCAL) measures the energy of “hadrons”, particles made of quarks and gluons (for example protons, neutrons, pions and kaons).
• Barrel_3_Solenoid_2.0.stl
  The solenoid magnet, formed by a cylindrical coil of superconducting fibres. When electricity (18,500 amps!) is circulated within these coils, they generate a magnetic field of around 4 tesla. This solenoid is the largest magnet of its type ever constructed.
• Barrel_2_Yoke.stl
  The steel yoke that confines the high magnetic field to the volume of the detector.
• Barrel_1_Muons_2.0.stl
  The muon chambers, one of the most important components of CMS. There are two different types of muon detectors in the barrel, Drift Tubes (DTs) and Resistive Plate Chambers (RPCs).
• Endcap_Full_2.0.stl and Endcap_Quarter_2.0.stl
  The endcaps "close" the ends of the barrel. They are made of alternating layers of steel yoke and muon chambers, composed of Cathode Strip Chambers (CSCs) and Resistive Plate Chambers (RPCs).
• HF_Full.stl and HF_Quarter.stl
  The Hadronic Forward calorimeters (HF), part of the HCAL system, pick up the myriad particles coming out of the collision region at shallow angles relative to the beam line.
• Airpad-16.stl
  A compressed-air powered piston system to lift the endcaps when moving them into position. Each pad can lift ~350 tonnes!
• Barrel_Feet-2.stl, Endcap_Feet-2.stl, HF_Riser-8.stl and HF_Table-2.stl
  Support structures.