Large Hadron Collider, abbreviated LHC, is the highest-energy particle accelerator in the world. A particle accelerator is a huge device designed to accelerate particles of matter called hadrons to extremely high energies and then collide them. Hadrons are subatomic particles (particles smaller than atoms) made up of even smaller particles called quarks and antiquarks. By studying the results of the collisions the LHC produces, scientists hope to learn more about the nature and properties of matter. The LHC is housed at CERN, the European Organization for Nuclear Research, outside of Geneva, Switzerland. Scientists started up the Large Hadron Collider in September 2008, but technical problems prevented them from conducting experiments. After a year of repairs and several months of testing, the LHC recorded a collision of two beams of protons at 7 trillion electronvolts (7 TeV) in 2010. One electronvolt is the energy needed to move an electron between two points with a potential difference of 1 volt.
The LHC is a type of ring-shaped particle accelerator known as a synchrotron. Particles in the LHC travel around a ring measuring nearly 17 miles (27 kilometers) in circumference. The high-energy hadrons in the LHC move at nearly the speed of light. The two beams of particles circulate in opposite directions through separate vacuum pipes. The LHC can accelerate two kinds of hadrons: protons and lead ions. The ions are atomic nuclei that have been stripped of electrons.
The LHC uses more than 9,000 superconducting magnets to steer and focus the beams of particles. Superconducting magnets conduct electric current with no loss of energy when operating at extremely low temperatures. They can produce extremely strong magnetic fields. A magnetic field is the influence that a magnet or electric current creates in the region around it. As particles in the ring gain speed, stronger magnetic forces are needed to keep them on their circular path. At the LHC’s highest energies, the superconducting magnets will produce magnetic fields more than 100,000 times as strong as Earth’s magnetic field.
The LHC guides the two particle beams into collisions at several places around the ring. At these locations, giant detectors record other particles produced by the collisions. On July 4, 2012, scientists at CERN announced significant evidence for a particle believed to be the Higgs boson. Some scientists think that interactions involving Higgs bosons give mass to all the other particles that have mass. Mass is a property that determines a particle’s resistance to acceleration. Evidence for the Higgs boson was collected by two separate experiments using the LHC. Scientists also hope that experiments at the LHC will help them develop theories of physics that improve upon the Standard Model. This model, the leading theory of subatomic particles and their interactions, fails to answer certain key questions in physics.
The LHC’s experiments have explored other aspects of the Standard Model as well. In 2015, scientists announced that they had discovered a rare, fleeting type of hadron called the pentaquark by analyzing measurements of the LHC’s earlier collisions. The pentaquark consists of five smaller particles in the form of a baryon and a meson. Three quarks combined make up a baryon. A quark linked to an antiquark makes up a meson. The existence of the pentaquark had been predicted by theory, but the particle had never been observed.
The LHC has twice entered long shutdowns to undergo maintenance and equipment upgrades. The collider did not conduct experiments from 2013 to 2015 or from 2018 to 2022. Another long shutdown is expected to begin in 2026. For that shutdown, CERN has planned major upgrades to transform the LHC into a more powerful collider known as the High-Luminosity Large Hadron Collider (HL-LHC).
