The Large Hadron Collider (LHC) at CERN is the largest and most powerful particle accelerator ever built. It accelerates protons to nearly the velocity of light — in clockwise and anti-clockwise directions — and then collides them at four locations around its ring. At these points, the energy of the particle collisions gets transformed into mass, spraying particles in all directions.
The Compact Muon Solenoid (or CMS) detector sits at one of these four collision points. It is a general-purpose detector; that is, it is designed to observe any new physics phenomena that the LHC might reveal.
To learn more, go to https://cms.cern/detector.