Compact Muon Solenoid
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 The accelerator chain of the Large Hadron Collider (LHC) |
|
| LHC experiments | |
| ATLAS | A Toroidal LHC ApparatuS |
| CMS | Compact Muon Solenoid |
| LHCb | LHC-beauty |
| ALICE | A Large Ion Collider Experiment |
| TOTEM | Total Cross Section, Elastic Scattering and Diffraction Dissociation |
| LHCf | LHC-forward |
| LHC preaccelerators | |
| p and Pb | Linear accelerator for proton and Lead |
| (not marked) | Proton Synchrotron Booster |
| PS | Proton Synchrotron |
| SPS | Super Proton Synchrotron |
The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors being (as of 2006) built on the proton-proton Large Hadron Collider (LHC) at CERN in Switzerland. Approximately 2300 people from 159 scientific institutes form the collaboration building it. It will be located in an underground chamber at Cessy in France, just across the border from Geneva. The completed detector will be cylindrical, 21 metres long and 16 metres diameter and weigh approximately 12500 tonnes.
Contents |
[edit] Goals
The main goals of the experiment are:
- Explore physics at the TeV scale
- The discovery of the Higgs boson
- To look for evidence of supersymmetry
- To be able to study aspects of heavy ion collisions
[edit] Highlights
The name highlights features of the detector:
- Its relatively small size
- The powerful solenoid
- Its optimization for tracking muons
[edit] Detector overview
CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 14 TeV, the center-of-mass energy of the LHC particle accelerator. It contains subsystems which are designed to measure the energy and momentum of photons, electrons, muons, and other products of the collisions. The innermost layer is a silicon-based tracker. Surrounding it is a scintillating crystal electromagnetic calorimeter, which is itself surrounded with a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMS solenoid which generates a powerful magnetic field of 4 T. Outside the magnet are the large muon detectors, which are inside the return yoke of the magnet.
[edit] The tracker
The main function of the tracker is to determine the trajectory of charged particles. Since the tracker sits inside the detector's magnetic field, there is a Lorenz force on any moving particle with electric charge. The radius of the helix described by such a particle can thus be used to calculate its momentum.
The tracker consists of almost 10 million silicon microstrips and 80 million pixel elements, totaling over 200 square meters of silicon. It is the largest device of its type ever constructed and thus it required many technological innovations to produce. The manufacture of the tracker necessitates strict quality control because once it is installed, it must operate smoothly for many years with few opportunities for maintenance.
The silicon strips and pixels are semiconductor devices with a large bias voltage across them and a depletion region in their active volume which is devoid of charge carriers. The passage of a charged particle creates free charge carriers (electrons and holes) in the depletion region. The electrons are attracted to a readout strip, where they produce a current that is amplified by electronics. If a particle passes through several of these detectors on its way through the tracker, the trajectory of the particle can be reconstructed.
[edit] The electromagnetic calorimeter
The electromagnetic calorimeter (ECAL) uses an active volume of about 80,000 lead tungstate crystals which are both extremely dense and very transparent. Electrons and photons interact with this material and cause a shower of radiation. This causes the crystal to scintillate, and the resulting light is picked up by photodetectors on the outside surfaces. The resulting electronic signals are digitized and can be used to reconstruct the energy of the incident particle.
[edit] The magnet
Like most particle physics detectors, CMS has a large solenoid. This allows the charge/mass ratio of particles to be determined from the curved track that they follow in the magnetic field. It is 13 metres long and 6 metres in diameter, and its refrigerated superconducting niobium-titanium coils will produce a 4-tesla magnetic field.
[edit] References
- Della Negra, Michel; Petrilli, Achille; Herve, Alain; Foa, Lorenzo; (2006). "CMS Physics Technical Design Report Volume I: Software and Detector Performance". CERN.
