Large Hadron Collider

Large Hadron Collider
Name	Large Hadron Collider
Caption	A section of the LHC tunnel.
Location	CERN
Coordinates	46, 14, 06, N...
Institution	CERN
Type	Synchrotron
Beam type	Protons, Lead nuclei
Target	Fixed target, colliding beams
Energy	6.8 TeV per beam (protons)
Circumference	26,659 m
Luminosity	2.06
Experiment	ATLAS, CMS, ALICE, LHCb, LHCf, TOTEM, MoEDAL
Dates	2008 – present

Large Hadron Collider. It is the world's most powerful and highest-energy particle accelerator, situated at the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. The facility primarily collides proton beams at unprecedented energies to probe the fundamental structure of matter and the universe, operating within a 26.7-kilometer LHC tunnel originally built for the Large Electron–Positron Collider. Its primary goals include testing predictions of the Standard Model, such as the existence of the Higgs boson, and searching for new physics like supersymmetry and dark matter.

Overview

The accelerator complex is the flagship project of CERN, forming the final link in a chain of pre-accelerators including the Proton Synchrotron and the Super Proton Synchrotron. It is designed to collide opposing beams of either protons or heavy ions, such as lead, at energies reaching several teraelectronvolts. The primary experiments are the general-purpose detectors ATLAS experiment and CMS experiment, alongside specialized installations like ALICE experiment for quark–gluon plasma studies and LHCb experiment investigating CP violation. Other smaller experiments include TOTEM, LHCf, and MoEDAL.

Design and construction

Approved in 1994, the project required an international collaboration of thousands of scientists and engineers, with major contributions from nations like France, Germany, the United Kingdom, and the United States. The design reused the existing LHC tunnel from the Large Electron–Positron Collider, necessitating the installation of a cryogenic system to cool over 1,200 superconducting magnets, primarily dipole magnets, to temperatures near absolute zero using liquid helium. Key technological challenges included achieving unprecedented magnetic fields to bend the beams and constructing ultra-high vacuum beam pipes. The final construction cost was approximately 4.3 billion Swiss francs.

Operational history

First beams were circulated on September 10, 2008, but an electrical fault caused a quench and significant damage to the magnet system, leading to a year-long shutdown for repairs. Collisions recommenced in November 2009 at reduced energy, with the first high-energy collisions at 3.5 TeV per beam achieved in March 2010. The machine reached its initial design energy of 6.5 TeV per beam in 2015. Major operational periods, known as Run 1 (2010–2013) and Run 2 (2015–2018), were separated by extended technical stops for upgrades. The Run 3 period began in July 2022.

Major discoveries and results

The most significant achievement was the joint discovery of a new particle consistent with the Higgs boson by the ATLAS experiment and CMS experiment on July 4, 2012, a feat for which theorists François Englert and Peter Higgs were awarded the Nobel Prize in Physics in 2013. Subsequent measurements have precisely determined its properties, confirming its role in the Brout–Englert–Higgs mechanism. Other major results include detailed studies of the quark–gluon plasma by ALICE experiment, observations of rare B meson decays by LHCb experiment, and stringent limits on theories like supersymmetry. No definitive evidence for dark matter particles has been found to date.

Technical specifications

The main ring has a circumference of 26,659 meters, with beams contained in two separate ultra-high vacuum pipes. It operates using 1,232 main dipole magnets and 392 quadrupole magnets, all made from niobium–titanium superconductor and cooled by a cryogenic system to 1.9 kelvins. For proton runs, the design center-of-mass energy is 13.6 TeV, with a peak luminosity exceeding 2×10³⁴ cm⁻²s⁻¹. In heavy-ion mode, it collides lead nuclei at a center-of-mass energy of 5.36 TeV per nucleon pair. The beams consist of up to 2,808 bunches, each containing over 100 billion particles.

Future upgrades

A major planned upgrade is the High Luminosity Large Hadron Collider (HL-LHC) project, scheduled for installation in the late 2020s, which aims to increase the integrated luminosity by a factor of ten. This will involve new technologies like advanced superconducting magnets, such as niobium–tin quadrupoles, and cutting-edge superconducting radio frequency cavities. These enhancements are essential for the ATLAS experiment and CMS experiment to collect sufficient data for studying rare Higgs boson processes and probing for subtle new physics beyond the Standard Model. Long-term concepts for a future Future Circular Collider at CERN are also under discussion.

Category:Particle accelerators Category:CERN Category:Buildings and structures in the canton of Geneva