The 27-kilometre ring, 100 metres under the Franco-Swiss border, where the Higgs boson was found (2008)
Beams cross the frontier thousands of times a second without a passport.
Science · Physics
The Large Hadron Collider
First beams 10 September 2008
Physics — particle accelerators
The Large Hadron Collider is the world's largest and most powerful particle accelerator, a 27-kilometre ring of superconducting magnets roughly 100 metres beneath the Franco-Swiss border near Geneva, operated by CERN. It reuses the tunnel dug for the earlier Large Electron–Positron Collider. Two counter-rotating beams of protons — or, in dedicated runs, lead ions — are steered by 1,232 dipole magnets cooled to 1.9 K with superfluid helium, and brought into collision at four points ringed by the detectors ATLAS, CMS, ALICE and LHCb. First beams circulated on 10 September 2008; nine days later a faulty electrical connection caused a magnet quench that shut the machine down for over a year. Its greatest result so far is the discovery of the Higgs boson in 2012.
How to spot them
- ▸A 27-kilometre ring about 100 m under the Franco-Swiss border, straddling two countries
- ▸Colder than outer space: 1.9 kelvin, kept there by superfluid helium
- ▸ATLAS, CMS and ALICE sit at three of its four collision points; a beauty-quark experiment at the fourth
- ▸Sued before switch-on by people who feared it would make a black hole and swallow the Earth
- ▸Inherited the tunnel of its electron–positron predecessor
Key facts
Home to the ATLAS, CMS and ALICE detectors, and to a fourth devoted to beauty quarks
ATLAS is the largest-volume detector ever built; CMS is the heaviest, at about 14,000 tonnes.
1,232 superconducting dipole magnets held at 1.9 K, colder than interstellar space
Superfluid helium carries the heat away; the cryogenic system is the largest in the world.
Shut down for over a year nine days after switch-on when a magnet quenched in 2008 (2008)
A faulty solder joint between two magnets vented six tonnes of helium into the tunnel.
Once halted, reportedly, by a bird dropping a piece of baguette on an outdoor substation (2009)
The bread caused an overheating incident in 2009; the machine was warm and not running beams.
The machine that collides protons at 13.6 TeV, the highest energy ever achieved in a laboratory
The design energy is 14 TeV; Run 3 has operated at 13.6 TeV since 2022.
Key ideas
- Colliding beams rather than firing at a fixed target puts all the energy into the collision, because the centre of mass is at rest.
- Protons are composite, so each collision is really a messy encounter between quarks and gluons at unpredictable energies — which is why the machine needs billions of collisions to find rare events.
- Lead-ion runs recreate the quark–gluon plasma, the state of matter thought to have filled the universe microseconds after the Big Bang.
Quick-fire facts
- •Circumference 26.7 km, about 100 m underground, near Geneva on the border between France and Switzerland
- •Built in the tunnel of LEP, the Large Electron–Positron Collider, which ran from 1989 to 2000
- •Design collision energy 14 TeV; it has run at 7, 8, 13 and 13.6 TeV
- •Beams cross about 40 million times a second at each of the four interaction points
- •The four main experiments are ATLAS, CMS, ALICE and LHCb; ATLAS and CMS jointly announced the Higgs boson on 4 July 2012
- •It is the coldest large region in the known universe at 1.9 K, below the 2.7 K of the cosmic microwave background
- •CERN also produced the World Wide Web: Tim Berners-Lee proposed it there in 1989
- •A 2008 lawsuit in Hawaii tried to stop the start-up over fears of micro black holes and strangelets; CERN's safety reviews found no risk
- •The 'Large Hadron Rap' by science writer Kate McAlpine went viral before the 2008 switch-on
- •A proposed successor, the Future Circular Collider, would run in a ring of about 91 km
Drill it — 8 cards
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Sources
- CERN — The Large Hadron Collider
- CERN — The Higgs boson For the 4 July 2012 ATLAS and CMS announcement.