The Large Hadron Collider is CERN’s 27-kilometer particle accelerator that circulates beams of protons or heavy ions in opposite directions and collides them so experiments can study matter at extremely high energies.
A 27-kilometer collider underground
The LHC sits in a circular tunnel near Geneva on the French-Swiss border. Superconducting magnets steer and focus particle beams while radio-frequency cavities add energy. The accelerator operates at temperatures and vacuum conditions engineered for extremely stable beams.
Particles first pass through a chain of smaller CERN accelerators before entering the LHC. Two beams then travel in opposite directions and are brought into collision at selected interaction points.
What the detectors see
ATLAS, CMS, ALICE and LHCb are major experiments around the ring. Their layered detectors record tracks, energy deposits and other signatures from particles produced in collisions. Most new particles decay too quickly to observe directly, so physicists reconstruct them from their decay products.
Enormous datasets are filtered and analyzed with global computing resources, and independent experiments can cross-check important discoveries.
What the LHC has discovered
The most famous result is the 2012 discovery of the Higgs boson by ATLAS and CMS. The collider also makes precision measurements of known particles, studies quark-gluon plasma in heavy-ion collisions, and searches for phenomena not predicted by the Standard Model.
Not finding a proposed new particle can also be scientifically valuable because it rules out regions of theoretical parameter space.
Run 3 and the High-Luminosity upgrade
CERN raised proton-proton collision energy to 13.6 TeV for Run 3. Physics production ended in June 2026, and the LHC entered Long Shutdown 3 later that month for the major upgrade toward the High-Luminosity LHC, which is scheduled to begin physics operation in 2030.
Higher luminosity means more collisions, not a new basic physical law. The goal is to measure known processes more precisely and increase the chance of seeing rare events.
