CMS experiment

CMS experiment. The Compact Muon Solenoid (CMS) experiment is one of the two large, general-purpose particle detectors constructed at the Large Hadron Collider (LHC) at CERN. It is designed to investigate a wide range of physics, including the properties of the Higgs boson, searches for dark matter, and evidence for supersymmetry. The international collaboration involves thousands of scientists and engineers from hundreds of institutes worldwide, operating a sophisticated detector renowned for its powerful solenoid magnet and precise muon detection system.

Overview

The experiment was conceived in the early 1990s alongside its counterpart, the ATLAS experiment, to fully exploit the discovery potential of the Large Hadron Collider. Its primary scientific motivation was to search for the Higgs boson, the particle associated with the Brout-Englert-Higgs mechanism, and to probe for physics beyond the Standard Model. Located at an underground cavern at the LHC interaction point near the French village of Cessy, it began recording proton–proton collision data in 2010. The detector's design emphasizes robust muon identification and measurement, which is crucial for many key physics channels, leading to its name.

Detector design

The detector is built in a cylindrical structure around the LHC beam pipe, organized in concentric layers like an onion. Its most distinctive feature is a massive, superconducting solenoid magnet that generates a powerful axial magnetic field of 3.8 tesla, bending the paths of charged particles for momentum measurement. From the innermost layer outward, key components include a silicon pixel detector and silicon strip tracker for precise vertexing and tracking, followed by a lead tungstate crystal electromagnetic calorimeter and a brass/scintillator hadronic calorimeter to measure particle energies. The outermost systems are the extensive muon spectrometer embedded in the iron flux return yoke, which also serves as a filter for identifying muons.

Physics goals and achievements

A central goal was the discovery and subsequent detailed study of the Higgs boson, which was achieved jointly with the ATLAS experiment in July 2012, a milestone recognized by the Nobel Prize in Physics awarded to François Englert and Peter Higgs. The collaboration has since made precise measurements of the boson's properties, including its mass, width, and couplings to other particles like the top quark and W and Z bosons. The experiment also conducts broad searches for new physics, such as supersymmetric particles, extra dimensions, and candidates for dark matter like weakly interacting massive particles. It has made significant contributions to quantum chromodynamics, studies of the quark–gluon plasma using heavy-ion collisions, and detailed measurements of top quark production and properties.

Collaboration and governance

The effort is managed by the CMS collaboration, a democratic body comprising over 5,000 particle physicists, engineers, technicians, and students from more than 200 institutes and universities in over 50 countries. Major contributing nations and regions include the United States, Germany, Italy, Russia, the United Kingdom, India, and members of CERN's European and international member states. Governance is executed through a Collaboration Board and a Spokesperson, who is elected by the collaboration, with technical and resource coordination handled by various institutional groups and funding agencies like the U.S. Department of Energy and the National Science Foundation.

Technical specifications

The detector is one of the largest scientific instruments ever built, with a length of 28.7 meters, a diameter of 15 meters, and a total weight of approximately 14,000 metric tons. The solenoid magnet stores an energy of 2.6 gigajoules. The inner tracking system covers an area of about 200 square meters of silicon sensors, while the electromagnetic calorimeter contains over 75,000 lead tungstate crystals. The muon system uses three different detector technologies: drift tubes, cathode strip chambers, and resistive plate chambers. The experiment's trigger system and computing grid, part of the worldwide LHC Computing Grid, process petabytes of data annually from billions of proton–proton collisions.

Category:Particle physics experiments Category:CERN experiments Category:Large Hadron Collider