The coldest racetrack on Earth
Beneath the French-Swiss countryside, 100 meters underground, lies the largest machine ever built. The Large Hadron Collider (LHC) is a 27-kilometer circular particle accelerator. Its purpose is to accelerate two beams of protons in opposite directions to nearly the speed of light. Each proton completes 11,245 laps of the ring every second. To keep these particles on their circular path, the LHC uses 1,232 superconducting dipole magnets, each 15 meters long and weighing 35 tonnes.
To achieve superconductivity, these magnets must be chilled to an operating temperature of 1.9 Kelvin (-271.3°C). This is colder than the 2.7 K temperature of empty outer space. A massive cryogenic system, the largest in the world, uses 120 tonnes of liquid helium to maintain this temperature. The proton beams travel inside two pipes kept at an ultra-high vacuum, emptier than the space between Earth and the Moon, to prevent the particles from colliding with stray gas molecules. protons begin in a simple bottle of hydrogen gas before passing through smaller accelerators—including the Proton Synchrotron and Super Proton Synchrotron—that build their energy before they are injected into the main LHC ring.
Recreating the Big Bang
At four specific points along the 27-kilometer ring, the two proton beams are made to cross paths, resulting in up to 600 million particle collisions per second. These collisions happen at a combined energy of 13.6 teraelectronvolts (TeV), creating conditions that have not existed since the first moments after the Big Bang. Surrounding these collision points are four enormous particle detectors: ATLAS, CMS, ALICE, and LHCb.
ATLAS and CMS are general-purpose detectors; ATLAS is the size of a six-story building. On July 4, 2012, scientists from both the ATLAS and CMS experiments announced the independent discovery of a new particle with a mass around 125 gigaelectronvolts (GeV). This was the Higgs boson, the particle that confirms the existence of the Higgs field, which gives fundamental particles their mass. Its discovery confirmed the final missing piece of the Standard Model of particle physics.
The ALICE experiment collides lead ions instead of protons to study quark-gluon plasma, a state of matter that existed for a few millionths of a second after the Big Bang. The LHCb experiment investigates the subtle differences between matter and antimatter by studying a type of particle called the "beauty quark." The data generated by these experiments is immense, originally producing about 15 petabytes annually, which is managed by the Worldwide LHC Computing Grid, a global network of over 170 computing centers in 42 countries.