MODEL RELEASED. CMS detector being built. The CMS (Compact Muon Solenoid) is a detector at the LHC (Large Hadron Collider), at CERN (the European particle physics laboratory) in Switzerland. This is the central part of the CMS under construction, which comprises a silicon-based particle tracker surrounded by electromagnetic and hadronic calorimeters for measuring particle energies. The CMS was lowered into position in an underground chamber at Cessy, France between 2006 and 2008 to surround part of the LHC, a 27-kilometre-long high-energy particle accelerator. The LHC is scheduled to start operating in summer 2008 and will endeavour to probe the inner structure of matter, in order to explain the origin of matter, dark matter and the mysteries of the early universe.