The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider.
It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries. It lies in a tunnel 27 kilometres in circumference and as deep as 175 metres beneath the France–Switzerland border near Geneva.
The first collisions were achieved in 2010 at an energy of 3.5 teraelectronvolts (TeV) per beam, about four times the previous world record. After upgrades it reached 6.5 TeV per beam (13 TeV total collision energy, the present world record). At the end of 2018, it was shut down for two years for further upgrades.
The collider has four crossing points where the accelerated particles collide. Seven detectors, each designed to detect different phenomena, are positioned around the crossing points. The LHC primarily collides proton beams, but it can also accelerate beams of heavy ions: lead–lead collisions and proton–lead collisions are typically performed for one month a year.
The LHC's goal is to allow physicists to test the predictions of different theories of particle physics, including measuring the properties of the Higgs boson searching for the large family of new particles predicted by supersymmetric theories, and other unresolved questions in particle physics.
The term hadron refers to subatomic composite particles composed of quarks held together by the strong force, as atoms and molecules are held together by the electromagnetic force.
More information: CERN
The best-known hadrons are the baryons such as protons and neutrons; hadrons also include mesons such as the pion and kaon, which were discovered during cosmic ray experiments in the late 1940s and early 1950s.
A collider is a type of a particle accelerator with two directed beams of particles. In particle physics, colliders are used as a research tool: they accelerate particles to very high kinetic energies and let them impact other particles.
Analysis of the byproducts of these collisions gives scientists good evidence of the structure of the subatomic world and the laws of nature governing it. Many of these byproducts are produced only by high-energy collisions, and they decay after very short periods of time. Thus many of them are hard or nearly impossible to study in other ways.
Many physicists hope that the Large Hadron Collider will help answer some of the fundamental open questions in physics, which concern the basic laws governing the interactions and forces among the elementary objects, the deep structure of space and time, and in particular the interrelation between quantum mechanics and general relativity.
Data are also needed from high-energy particle experiments to suggest which versions of current scientific models are more likely to be correct -in particular to choose between the Standard Model and Higgsless model and to validate their predictions and allow further theoretical development.
The
collider is contained in a circular tunnel, with a circumference of
26.7 kilometres, at a depth ranging from 50 to 175 metres underground.
The variation in depth was deliberate, to reduce the amount of tunnel
that lies under the Jura Mountains to avoid having to excavate a
vertical access shaft there.
More information: Atlas Obscura
A tunnel was chosen to avoid having to purchase expensive land on the surface, which would also have an impact on the landscape and to take advantage of the shielding against background radiation that the earth's crust provides.
The LHC first went live on 10 September 2008, but initial testing was delayed for 14 months from 19 September 2008 to 20 November 2009, following a magnet quench incident that caused extensive damage to over 50 superconducting magnets, their mountings, and the vacuum pipe.
During its first run (2010–2013), the LHC collided two opposing particle beams of either protons at up to 4 teraelectronvolts (4 TeV or 0.64 microjoules), or lead nuclei (574 TeV per nucleus, or 2.76 TeV per nucleon).
Its first run discoveries included the long-sought Higgs boson, several composite particles (hadrons) like the χb (3P) bottomonium state, the first creation of a quark-gluon plasma, and the first observations of the very rare decay of the Bs meson into two muons (Bs0 → μ+μ−), which challenged the validity of existing models of supersymmetry.
An initial focus of research was to investigate the possible existence of the Higgs boson, a key part of the Standard Model of physics which is predicted by theory, but had not yet been observed before due to its high mass and elusive nature.
CERN scientists estimated that, if the Standard Model were correct, the LHC would produce several Higgs bosons every minute, allowing physicists to finally confirm or disprove the Higgs boson's existence. In addition, the LHC allowed the search for supersymmetric particles and other hypothetical particles as possible unknown areas of physics.
Some extensions of the Standard Model predict additional particles, such as the heavy W' and Z' gauge bosons, which are also estimated to be within reach of the LHC to discover.
More information: Nature
Science is a way of life.
Science is a perspective.
Science is the process that takes us from confusion
to understanding in a manner that's precise, predictive and reliable
-a transformation, for those lucky enough to experience it,
that is empowering and emotional.
Brian Greene
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