Large Hadron Collider
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The Large Hadron Collider (LHC) is the world's largest and highest-energy
particle collider A collider is a type of particle accelerator which brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators. Colliders are used as a research tool in particle ...
. It was built by the
European Organization for Nuclear Research The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...
(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 in circumference and as deep as beneath the France–Switzerland border near
Geneva Geneva ( ; french: Genève ) frp, Genèva ; german: link=no, Genf ; it, Ginevra ; rm, Genevra is the List of cities in Switzerland, second-most populous city in Switzerland (after Zürich) and the most populous city of Romandy, the French-speaki ...
. The first collisions were achieved in 2010 at an energy of 3.5 
tera TERA is a shielded twisted pair connector for use with Category 7 twisted-pair data cables, developed by The Siemon Company and standardised in 2003 by the International Electrotechnical Commission (IEC) with the reference IEC 61076-3-104. Th ...
electronvolt In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defi ...
s (TeV) per beam, about four times the previous world record. After upgrades it reached 6.5 TeV per beam (13 TeV total collision energy). At the end of 2018, it was shut down for three 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 An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
:
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
–lead collisions and
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
–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 Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
, 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.


Background

The term ''
hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the e ...
'' refers to
subatomic In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a pro ...
composite particle This is a list of known and hypothesized particles. Elementary particles Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles. They are the fundamental ob ...
s composed of quarks held together by the
strong force The strong interaction or strong force is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called the n ...
(analogous to the way that
atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and ...
s and
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
s are held together by the
electromagnetic force In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of ...
). The best-known hadrons are the
baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classif ...
s such as
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s and
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s; hadrons also include
meson In particle physics, a meson ( or ) is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles ...
s such as the
pion In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: ) is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more gene ...
and
kaon KAON (Karlsruhe ontology) is an ontology infrastructure developed by the University of Karlsruhe and the Research Center for Information Technologies in Karlsruhe. Its first incarnation was developed in 2002 and supported an enhanced version of ...
, which were discovered during
cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
experiments in the late 1940s and early 1950s. A ''
collider A collider is a type of particle accelerator which brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators. Colliders are used as a research tool in particl ...
'' is a type of a
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...
which brings two opposing
particle In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from ...
beams together such that the particles collide. In
particle physics Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
, colliders, though harder to construct, are a powerful research tool because they reach a much higher
center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...
energy than fixed target setups. Analysis of the byproducts of these collisions gives scientists good evidence of the structure of the
subatomic In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a pro ...
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.


Purpose

Many
physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...
s 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 Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...
and
general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
. Data are also needed from
high-energy particle Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and b ...
experiments to suggest which versions of current scientific models are more likely to be correct – in particular to choose between the
Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
and
Higgsless model The Alternative models to the Standard Higgs Model are models which are considered by many particle physicists to solve some of the Higgs boson's existing problems. Two of the most currently researched models are quantum triviality, and Higgs hie ...
and to validate their predictions and allow further theoretical development. Issues explored by LHC collisions include: * Is the
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
of
elementary particle In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. Particles currently thought to be elementary include electrons, the fundamental fermions ( quarks, leptons, an ...
s being generated by the
Higgs mechanism In the Standard Model of particle physics, the Higgs mechanism is essential to explain the generation mechanism of the property "mass" for gauge bosons. Without the Higgs mechanism, all bosons (one of the two classes of particles, the other be ...
via
electroweak In particle physics, the electroweak interaction or electroweak force is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction. Although these two forces appear very differe ...
symmetry breaking In physics, symmetry breaking is a phenomenon in which (infinitesimally) small fluctuations acting on a system crossing a critical point decide the system's fate, by determining which branch of a bifurcation is taken. To an outside observe ...
? It was expected that the collider experiments will either demonstrate or rule out the existence of the elusive Higgs boson, thereby allowing physicists to consider whether the Standard Model or its Higgsless alternatives are more likely to be correct."Accordingly, in common with many of my colleagues, I think it highly likely that both the Higgs boson and other new phenomena will be found with the LHC."..."This mass threshold means, among other things, that something new – either a Higgs boson or other novel phenomena – is to be found when the LHC turns the thought experiment into a real one." * Is
supersymmetry In a supersymmetric theory the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theories e ...
, an extension of the Standard Model and Poincaré symmetry, realized in nature, implying that all known particles have supersymmetric partners? * Are there
extra dimensions In physics, extra dimensions are proposed additional space or time dimensions beyond the (3 + 1) typical of observed spacetime, such as the first attempts based on the Kaluza–Klein theory. Among theories proposing extra dimensions are: ...
, as predicted by various models based on
string theory In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interac ...
, and can we detect them? * What is the nature of the
dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not a ...
that appears to account for 27% of the mass–energy of the
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...
? Other open questions that may be explored using high-energy particle collisions: * It is already known that
electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of ...
and the
weak nuclear force In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction ...
are different manifestations of a single force called the electroweak force. The LHC may clarify whether the electroweak force and the
strong nuclear force The strong interaction or strong force is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called the ...
are similarly just different manifestations of one universal unified force, as predicted by various Grand Unification Theories. * Why is the fourth fundamental force (
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
) so many orders of magnitude weaker than the other three
fundamental forces In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four fundamental interactions known to exist: the gravitational and electro ...
? See also
Hierarchy problem In theoretical physics, the hierarchy problem is the problem concerning the large discrepancy between aspects of the weak force and gravity. There is no scientific consensus on why, for example, the weak force is 1024 times stronger than gravit ...
. * Are there additional sources of quark flavour mixing, beyond those already present within the
Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
? * Why are there apparent violations of the
symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...
between matter and
antimatter In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter. Antimatter occurs in natural processes like cosmic ray collisions and some types of radioac ...
? See also
CP violation In particle physics, CP violation is a violation of CP-symmetry (or charge conjugation parity symmetry): the combination of C-symmetry (charge symmetry) and P-symmetry ( parity symmetry). CP-symmetry states that the laws of physics should be th ...
. * What are the nature and properties of
quark–gluon plasma Quark–gluon plasma (QGP) or quark soup is an interacting localized assembly of quarks and gluons at thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasma'' signals that free color charges are allowed. In a ...
, thought to have existed in the
early universe The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, wit ...
and in certain
compact Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to: * Interstate compact * Blood compact, an ancient ritual of the Philippines * Compact government, a type of colonial rule utilized in British ...
and strange astronomical objects today? This will be investigated by ''heavy ion collisions'', mainly in ALICE, but also in
CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color manag ...
,
ATLAS An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
and
LHCb The LHCb (Large Hadron Collider beauty) experiment is one of eight particle physics detector experiments collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the paramet ...
. First observed in 2010, findings published in 2012 confirmed the phenomenon of jet quenching in heavy-ion collisions.


Design

The collider is contained in a circular tunnel, with a circumference of , at a depth ranging from underground. The variation in depth was deliberate, to reduce the amount of tunnel that lies under the
Jura Mountains The Jura Mountains ( , , , ; french: Massif du Jura; german: Juragebirge; it, Massiccio del Giura, rm, Montagnas da Jura) are a sub-alpine mountain range a short distance north of the Western Alps and mainly demarcate a long part of the Frenc ...
to avoid having to excavate a vertical access shaft there. 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 wide concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the
Large Electron–Positron Collider The Large Electron–Positron Collider (LEP) was one of the largest particle accelerators ever constructed. It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland. LEP collided elect ...
. The tunnel crosses the border between Switzerland and France at four points, with most of it in France. Surface buildings hold ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants. The collider tunnel contains two adjacent parallel
beamline In accelerator physics, a beamline refers to the trajectory of the beam of particles, including the overall construction of the path segment (guide tubes, diagnostic devices) along a specific path of an accelerator facility. This part is either ...
s (or ''beam pipes'') each containing a beam, which travel in opposite directions around the ring. The beams intersect at four points around the ring, which is where the particle collisions take place. Some 1,232
dipole magnet A dipole magnet is the simplest type of magnet. It has two poles, one north and one south. Its magnetic field lines form simple closed loops which emerge from the north pole, re-enter at the south pole, then pass through the body of the magnet. ...
s keep the beams on their circular path (see image), while an additional 392
quadrupole magnet Quadrupole magnets, abbreviated as Q-magnets, consist of groups of four magnets laid out so that in the planar multipole expansion of the field, the dipole terms cancel and where the lowest significant terms in the field equations are quadrupole. ...
s are used to keep the beams focused, with stronger quadrupole magnets close to the intersection points in order to maximize the chances of interaction where the two beams cross. Magnets of higher multipole orders are used to correct smaller imperfections in the field geometry. In total, about 10,000 superconducting magnets are installed, with the dipole magnets having a mass of over 27 tonnes. Approximately 96 tonnes of superfluid helium-4 is needed to keep the magnets, made of copper-clad niobium-titanium, at their
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
of , making the LHC the largest cryogenic facility in the world at liquid helium temperature. LHC uses 470 tonnes of Nb–Ti superconductor. During LHC operations, the CERN site draws roughly 200 MW of electrical power from the French
electrical grid An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
, which, for comparison, is about one-third the energy consumption of the city of Geneva; the LHC accelerator and detectors draw about 120 MW thereof. Each day of its operation generates 140
terabyte The byte is a units of information, unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character (computing), character of text in a computer and for this ...
s of data. When running an energy of 6.5 TeV per proton, once or twice a day, as the protons are accelerated from 450 
GeV GEV may refer to: * ''G.E.V.'' (board game), a tabletop game by Steve Jackson Games * Ashe County Airport, in North Carolina, United States * Gällivare Lapland Airport, in Sweden * Generalized extreme value distribution * Gev Sella, Israeli-Sou ...
to 6.5  TeV, the field of the superconducting dipole magnets is increased from 0.54 to . The protons each have an
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
of 6.5 TeV, giving a total collision energy of 13 TeV. At this energy, the protons have a
Lorentz factor The Lorentz factor or Lorentz term is a quantity expressing how much the measurements of time, length, and other physical properties change for an object while that object is moving. The expression appears in several equations in special relativit ...
of about 6,930 and move at about , or about slower than the
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
(''c''). It takes less than for a proton to travel 26.7 km around the main ring. This results in per second for protons whether the particles are at low or high energy in the main ring, since the speed difference between these energies is beyond the fifth decimal. Rather than having continuous beams, the protons are bunched together, into up to , with in each bunch so that interactions between the two beams take place at discrete intervals, mainly apart, providing a bunch collision rate of 40 MHz. It was operated with fewer bunches in the first years. The design
luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
of the LHC is 1034 cm−2s−1, which was first reached in June 2016. By 2017, twice this value was achieved. Before being injected into the main accelerator, the particles are prepared by a series of systems that successively increase their energy. The first system is the
linear particle accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear b ...
Linac4 generating 160 MeV negative hydrogen ions (H ions), which feeds the
Proton Synchrotron Booster The Proton Synchrotron Booster (PSB) is the first and smallest circular proton accelerator (a synchrotron) in the accelerator chain at the CERN injection complex, which also provides beams to the Large Hadron Collider. It contains four sup ...
(PSB). There, both electrons are stripped from the hydrogen ions leaving only the nucleus containing one proton. Protons are then accelerated to 2 GeV and injected into the
Proton Synchrotron The Proton Synchrotron (PS, sometimes also referred to as CPS) is a particle accelerator at CERN. It is CERN's first synchrotron, beginning its operation in 1959. For a brief period the PS was the world's highest energy particle accelerator. It ...
(PS), where they are accelerated to 26 GeV. Finally, the Super Proton Synchrotron (SPS) is used to increase their energy further to 450 GeV before they are at last injected (over a period of several minutes) into the main ring. Here, the proton bunches are accumulated, accelerated (over a period of ) to their peak energy, and finally circulated for 5 to while collisions occur at the four intersection points. The LHC physics programme is mainly based on proton–proton collisions. However, during shorter running periods, typically one month per year, heavy-ion collisions are included in the programme. While lighter ions are considered as well, the baseline scheme deals with
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
ions (see A Large Ion Collider Experiment). The lead ions are first accelerated by the linear accelerator LINAC 3, and the
Low Energy Ion Ring The Low Energy Ion Ring (LEIR) is a particle accelerator at CERN used to accelerate ions from the LINAC 3 to the Proton Synchrotron (PS) to provide ions for collisions within the Large Hadron Collider (LHC). History LEIR was converted from ...
(LEIR) is used as an ion storage and cooler unit. The ions are then further accelerated by the PS and SPS before being injected into LHC ring, where they reach an energy of 2.3 TeV per
nucleon In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...
(or 522 TeV per ion), higher than the energies reached by the
Relativistic Heavy Ion Collider The Relativistic Heavy Ion Collider (RHIC ) is the first and one of only two operating heavy-ion colliders, and the only spin-polarized proton collider ever built. Located at Brookhaven National Laboratory (BNL) in Upton, New York, and used by a ...
. The aim of the heavy-ion programme is to investigate
quark–gluon plasma Quark–gluon plasma (QGP) or quark soup is an interacting localized assembly of quarks and gluons at thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasma'' signals that free color charges are allowed. In a ...
, which existed in the
early universe The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, wit ...
.


Detectors

Nine detectors have been constructed at the LHC, located underground in large caverns excavated at the LHC's intersection points. Two of them, the
ATLAS experiment ATLAS is the largest general-purpose particle detector experiment at the Large Hadron Collider (LHC), a particle accelerator at CERN (the European Organization for Nuclear Research) in Switzerland. The experiment is designed to take advantage of ...
and the
Compact Muon Solenoid The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France. The goal of the CMS experiment is to investigate a wide range ...
(CMS), are large general-purpose
particle detector In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing particles, such as those produced by nuc ...
s. ALICE and
LHCb The LHCb (Large Hadron Collider beauty) experiment is one of eight particle physics detector experiments collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the paramet ...
have more specialized roles and the other five,
TOTEM A totem (from oj, ᑑᑌᒼ, italics=no or ''doodem'') is a spirit being, sacred object, or symbol that serves as an emblem of a group of people, such as a family, clan, lineage, or tribe, such as in the Anishinaabe clan system. While ''the wo ...
,
MoEDAL MoEDAL (Monopole and Exotics Detector at the LHC) is a particle physics experiment at the Large Hadron Collider (LHC). Experiment MoEDAL shares the cavern at Point 8 with LHCb, and its prime goal is to directly search for the magnetic monopole (M ...
, LHCf, SND and FASER, are much smaller and are for very specialized research. The ATLAS and CMS experiments discovered the Higgs boson, which is strong evidence that the Standard Model has the correct mechanism of giving mass to elementary particles.


Computing and analysis facilities

Data produced by LHC, as well as LHC-related simulation, were estimated at approximately 15
petabyte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
s per year (max throughput while running is not stated)—a major challenge in its own right at the time. The
LHC Computing Grid The Worldwide LHC Computing Grid (WLCG), formerly (until 2006) the LHC Computing Grid (LCG), is an international collaborative project that consists of a grid-based computer network infrastructure incorporating over 170 computing centers in 42 co ...
was constructed as part of the LHC design, to handle the massive amounts of data expected for its collisions. It is an international collaborative project that consists of a grid-based
computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
infrastructure initially connecting 140 computing centres in 35 countries (over 170 in 36 countries ). It was designed by
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...
to handle the significant volume of data produced by LHC experiments, incorporating both private fibre optic cable links and existing high-speed portions of the public
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
to enable data transfer from CERN to academic institutions around the world. The
Open Science Grid The Open Science Grid Consortium is an organization that administers a worldwide grid of technological resources called the Open Science Grid, which facilitates distributed computing for scientific research. Founded in 2004, the consortium is com ...
is used as the primary infrastructure in the United States, and also as part of an interoperable federation with the LHC Computing Grid. The
distributed computing A distributed system is a system whose components are located on different computer network, networked computers, which communicate and coordinate their actions by message passing, passing messages to one another from any system. Distributed com ...
project
LHC@home LHC@home is a volunteer computing project researching particle physics that uses the Berkeley Open Infrastructure for Network Computing (BOINC) platform. The project's computing power is utilized by physicists at CERN in support of the Large ...
was started to support the construction and calibration of the LHC. The project uses the
BOINC The Berkeley Open Infrastructure for Network Computing (BOINC, pronounced – rhymes with "oink") is an open-source middleware system for volunteer computing (a type of distributed computing). Developed originally to support SETI@home, it beca ...
platform, enabling anybody with an Internet connection and a computer running
Mac OS X macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...
,
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
or
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
to use their computer's idle time to simulate how particles will travel in the beam pipes. With this information, the scientists are able to determine how the magnets should be calibrated to gain the most stable "orbit" of the beams in the ring. In August 2011, a second application (Test4Theory) went live which performs simulations against which to compare actual test data, to determine confidence levels of the results. By 2012, data from over 6 quadrillion () LHC proton–proton collisions had been analysed, LHC collision data was being produced at approximately 25
petabyte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
s per year, and the LHC Computing Grid had become the world's largest computing grid in 2012, comprising over 170 computing facilities in a worldwide network across 36 countries.


Operational history

The LHC first went operational on 10 September 2008, but initial testing was delayed for 14 months from 19 September 2008 to 20 November 2009, following a
magnet quench A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
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 A particle beam is a stream of charged or neutral particles. In particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between the creation and control of charged particle beams and neu ...
of either
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s at up to 4  teraelectronvolts or , or
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
nuclei (574 TeV per nucleus, or 2.76 TeV per
nucleon In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...
). Its first run discoveries included the long-sought Higgs boson, several composite particles (
hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the e ...
s) like the χb (3P)
bottomonium In particle physics, quarkonium (from quark and -onium, pl. quarkonia) is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it both a neutral particle and its own antiparticle. Light quarks Light quarks ( up ...
state, the first creation of a
quark–gluon plasma Quark–gluon plasma (QGP) or quark soup is an interacting localized assembly of quarks and gluons at thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasma'' signals that free color charges are allowed. In a ...
, 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 In a supersymmetric theory the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theories e ...
.


Construction


Operational challenges

The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of the amount of energy stored in the magnets and the beams. While operating, the total energy stored in the magnets is and the total energy carried by the two beams reaches . Loss of only one ten-millionth part (10−7) of the beam is sufficient to
quench In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as p ...
a superconducting magnet, while each of the two
beam dump A beam dump, also known as a beam block, a beam stop, or a beam trap, is a device designed to absorb the energy of photons or other particles within an energetic beam. Types of beam dumps Beam blocks Beam blocks are simple optical elements ...
s must absorb . These energies are carried by very little matter: under nominal operating conditions (2,808 bunches per beam, 1.15×1011 protons per bunch), the beam pipes contain 1.0×10−9 gram of hydrogen, which, in standard conditions for temperature and pressure, would fill the volume of one grain of fine sand.


Cost

With a budget of €7.5 billion (approx. $9bn or £6.19bn ), the LHC is one of the most expensive scientific instruments ever built. The total cost of the project is expected to be of the order of 4.6bn
Swiss franc The Swiss franc is the currency and legal tender of Switzerland and Liechtenstein. It is also legal tender in the Italian exclave of Campione d'Italia which is surrounded by Swiss territory. The Swiss National Bank (SNB) issues banknotes and the f ...
s (SFr) (approx. $4.4bn, €3.1bn, or £2.8bn ) for the accelerator and 1.16bn (SFr) (approx. $1.1bn, €0.8bn, or £0.7bn ) for the CERN contribution to the experiments. The construction of LHC was approved in 1995 with a budget of SFr 2.6bn, with another SFr 210M toward the experiments. However, cost overruns, estimated in a major review in 2001 at around SFr 480M for the accelerator, and SFr 50M for the experiments, along with a reduction in CERN's budget, pushed the completion date from 2005 to April 2007. The superconducting magnets were responsible for SFr 180M of the cost increase. There were also further costs and delays owing to engineering difficulties encountered while building the cavern for the
Compact Muon Solenoid The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France. The goal of the CMS experiment is to investigate a wide range ...
, and also due to magnet supports which were insufficiently strongly designed and failed their initial testing (2007) and damage from a
magnet quench A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
and
liquid helium Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...
escape (inaugural testing, 2008) ''(see: Construction accidents and delays)''. Because electricity costs are lower during the summer, the LHC normally does not operate over the winter months, although exceptions over the 2009/10 and 2012/2013 winters were made to make up for the 2008 start-up delays and to improve precision of measurements of the new particle discovered in 2012, respectively.


Construction accidents and delays

* On 25 October 2005, José Pereira Lages, a technician, was killed in the LHC when a
switchgear In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be ...
that was being transported fell on top of him. * On 27 March 2007, a cryogenic magnet support designed and provided by
Fermilab Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operat ...
and
KEK , known as KEK, is a Japanese organization whose purpose is to operate the largest particle physics laboratory in Japan, situated in Tsukuba, Ibaraki prefecture. It was established in 1997. The term "KEK" is also used to refer to the laboratory ...
broke during an initial pressure test involving one of the LHC's inner triplet (focusing quadrupole) magnet assemblies. No one was injured. Fermilab director Pier Oddone stated "In this case we are dumbfounded that we missed some very simple balance of forces". The fault had been present in the original design, and remained during four engineering reviews over the following years. Analysis revealed that its design, made as thin as possible for better insulation, was not strong enough to withstand the forces generated during pressure testing. Details are available in a statement from Fermilab, with which CERN is in agreement. Repairing the broken magnet and reinforcing the eight identical assemblies used by LHC delayed the start-up date, then planned for November 2007. * On 19 September 2008, during initial testing, a faulty electrical connection led to a
magnet quench A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
(the sudden loss of a superconducting magnet's superconducting ability owing to warming or
electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
effects). Six tonnes of supercooled
liquid helium Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...
—used to cool the magnets—escaped, with sufficient force to break 10-ton magnets nearby from their mountings, and caused considerable damage and contamination of the vacuum tube. Repairs and safety checks caused a delay of around 14 months. * Two vacuum leaks were found in July 2009, and the start of operations was further postponed to mid-November 2009.


Exclusion of Russia

With the 2022 invasion of
Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...
by
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, the participation of Russians with CERN was called into question. Approximately 8% of the workforce are of Russian nationality. In June 2022 CERN said the governing council "intends to terminate" CERN's cooperation agreements with Belarus and Russia when they expire, respectively in June and December 2024. CERN said it would monitor developments in Ukraine and remains prepared to take additional steps as warranted. CERN further said that it would reduce the Ukrainian contribution to CERN for 2022 to the amount already remitted to the Organization, thereby waiving the second instalment of the contribution.


Initial lower magnet currents

In both of its runs (2010 to 2012 and 2015), the LHC was initially run at energies below its planned operating energy, and ramped up to just 2 x 4 TeV energy on its first run and 2 x 6.5 TeV on its second run, below the design energy of 2 x 7 TeV. This is because massive superconducting magnets require considerable magnet training to handle the high currents involved without losing their superconducting ability, and the high currents are necessary to allow a high proton energy. The "training" process involves repeatedly running the magnets with lower currents to provoke any quenches or minute movements that may result. It also takes time to cool down magnets to their operating temperature of around 1.9 K (close to absolute zero). Over time the magnet "beds in" and ceases to quench at these lesser currents and can handle the full design current without quenching; CERN media describe the magnets as "shaking out" the unavoidable tiny manufacturing imperfections in their crystals and positions that had initially impaired their ability to handle their planned currents. The magnets, over time and with training, gradually become able to handle their full planned currents without quenching.


Inaugural tests (2008)

The first beam was circulated through the
collider A collider is a type of particle accelerator which brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators. Colliders are used as a research tool in particl ...
on the morning of 10 September 2008.
CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...
successfully fired the protons around the tunnel in stages, three kilometres at a time. The particles were fired in a clockwise direction into the accelerator and successfully steered around it at 10:28 local time. The LHC successfully completed its major test: after a series of trial runs, two white dots flashed on a computer screen showing the protons travelled the full length of the collider. It took less than one hour to guide the stream of particles around its inaugural circuit. CERN next successfully sent a beam of protons in an anticlockwise direction, taking slightly longer at one and a half hours owing to a problem with the
cryogenics In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
, with the full circuit being completed at 14:59.


Quench incident

On 19 September 2008, a
magnet quench A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
occurred in about 100 bending
magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
s in sectors 3 and 4, where an electrical fault led to a loss of approximately six tonnes of
liquid helium Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...
(the magnets' cryogenic coolant), which was vented into the tunnel. The escaping vapour expanded with explosive force, damaging a total of 53 superconducting magnets and their mountings, and contaminating the vacuum pipe, which also lost vacuum conditions. Shortly after the incident, CERN reported that the most likely cause of the problem was a faulty electrical connection between two magnets, and that – owing to the time needed to warm up the affected sectors and then cool them back down to operating temperature – it would take at least two months to fix. CERN released an interim technical report and preliminary analysis of the incident on 15 and 16 October 2008 respectively, and a more detailed report on 5 December 2008. The analysis of the incident by CERN confirmed that an electrical fault had indeed been the cause. The faulty electrical connection had led (correctly) to a
failsafe In engineering, a fail-safe is a design feature or practice that in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safe ...
power abort of the electrical systems powering the superconducting magnets, but had also caused an
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma (p ...
(or discharge) which damaged the integrity of the supercooled helium's enclosure and vacuum insulation, causing the coolant's temperature and pressure to rapidly rise beyond the ability of the safety systems to contain it, and leading to a temperature rise of about 100 degrees Celsius in some of the affected magnets. Energy stored in the superconducting magnets and
electrical noise In electronics, noise is an unwanted disturbance in an electrical signal. Noise generated by electronic devices varies greatly as it is produced by several different effects. In particular, noise is inherent in physics, and central to the ...
induced in other quench detectors also played a role in the rapid heating. Around two
tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s of liquid helium escaped explosively before detectors triggered an emergency stop, and a further four tonnes leaked at lower pressure in the aftermath. A total of 53 magnets were damaged in the incident and were repaired or replaced during the winter shutdown. This accident was thoroughly discussed in a 22 February 2010 ''Superconductor Science and Technology'' article by CERN physicist
Lucio Rossi Lucio Rossi (born 24 September 1955) is an Italian physicist who is working in the field of superconductivity. He has been working since 2001 at CERN, on leave from the University of Milan, where he directed the Magnets & Superconductors for the ...
. In the original schedule for LHC commissioning, the first "modest" high-energy collisions at a centre-of-mass energy of 900 GeV were expected to take place before the end of September 2008, and the LHC was expected to be operating at 10 TeV by the end of 2008. However, owing to the delay caused by the incident, the collider was not operational until November 2009. Despite the delay, LHC was officially inaugurated on 21 October 2008, in the presence of political leaders, science ministers from CERN's 20 Member States, CERN officials, and members of the worldwide scientific community. Most of 2009 was spent on repairs and reviews from the damage caused by the quench incident, along with two further vacuum leaks identified in July 2009; this pushed the start of operations to November of that year.


Run 1: first operational run (2009–2013)

On 20 November 2009, low-energy beams circulated in the tunnel for the first time since the incident, and shortly after, on 30 November, the LHC achieved 1.18 TeV per beam to become the world's highest-energy particle accelerator, beating the
Tevatron The Tevatron was a circular particle accelerator (active until 2011) in the United States, at the Fermi National Accelerator Laboratory (also known as ''Fermilab''), east of Batavia, Illinois, and is the second highest energy particle collider ...
's previous record of 0.98 TeV per beam held for eight years. The early part of 2010 saw the continued ramp-up of beam in energies and early physics experiments towards 3.5 TeV per beam and on 30 March 2010, LHC set a new record for high-energy collisions by colliding proton beams at a combined energy level of 7 TeV. The attempt was the third that day, after two unsuccessful attempts in which the protons had to be "dumped" from the collider and new beams had to be injected. This also marked the start of the main research programme. The first proton run ended on 4 November 2010. A run with lead ions started on 8 November 2010, and ended on 6 December 2010, allowing the ALICE experiment to study matter under extreme conditions similar to those shortly after the Big Bang. CERN originally planned that the LHC would run through to the end of 2012, with a short break at the end of 2011 to allow for an increase in beam energy from 3.5 to 4 TeV per beam. At the end of 2012, the LHC was planned to be temporarily shut down until around 2015 to allow upgrade to a planned beam energy of 7 TeV per beam. In late 2012, in light of the July 2012 discovery of the Higgs boson, the shutdown was postponed for some weeks into early 2013, to allow additional data to be obtained before shutdown.


Long Shutdown 1 (2013–2015)

The LHC was shut down on 13 February 2013 for its 2-year upgrade called Long Shutdown 1 (LS1), which was to touch on many aspects of the LHC: enabling collisions at 14 TeV, enhancing its detectors and pre-accelerators (the Proton Synchrotron and Super Proton Synchrotron), as well as replacing its ventilation system and of cabling impaired by high-energy collisions from its first run. The upgraded collider began its long start-up and testing process in June 2014, with the Proton Synchrotron Booster starting on 2 June 2014, the final interconnection between magnets completing and the Proton Synchrotron circulating particles on 18 June 2014, and the first section of the main LHC supermagnet system reaching operating temperature of , a few days later. Due to the slow progress with "training" the superconducting magnets, it was decided to start the second run with a lower energy of 6.5 TeV per beam, corresponding to a current of 11,000
ampere The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...
s. The first of the main LHC magnets were reported to have been successfully trained by 9 December 2014, while training the other magnet sectors was finished in March 2015.


Run 2: second operational run (2015–2018)

On 5 April 2015, the LHC restarted after a two-year break, during which the electrical connectors between the bending magnets were upgraded to safely handle the current required for 7 TeV per beam (14 TeV collision energy). However, the bending magnets were only
trained Training is teaching, or developing in oneself or others, any skills and knowledge or fitness that relate to specific useful competencies. Training has specific goals of improving one's capability, capacity, productivity and performance. I ...
to handle up to 6.5 TeV per beam (13 TeV collision energy), which became the operating energy for 2015 to 2018. The energy was first reached on 10 April 2015. The upgrades culminated in colliding protons together with a combined energy of 13 TeV. On 3 June 2015, the LHC started delivering physics data after almost two years offline. In the following months, it was used for proton–proton collisions, while in November, the machine switched to collisions of lead ions and in December, the usual winter shutdown started. In 2016, the machine operators focused on increasing the luminosity for proton–proton collisions. The design value was first reached 29 June, and further improvements increased the collision rate to 40% above the design value. The total number of collisions in 2016 exceeded the number from Run 1 – at a higher energy per collision. The proton–proton run was followed by four weeks of proton–lead collisions. In 2017, the luminosity was increased further and reached twice the design value. The total number of collisions was higher than in 2016 as well. The 2018 physics run began on 17 April and stopped on 3 December, including four weeks of lead–lead collisions.


Long Shutdown 2 (2018–2022)

Long Shutdown 2 (LS2) started on 10 December 2018. The LHC and the whole CERN accelerator complex was maintained and upgraded. The goal of the upgrades was to implement the
High Luminosity Large Hadron Collider The High Luminosity Large Hadron Collider (HL-LHC; formerly referred to as HiLumi LHC) is an upgrade to the Large Hadron Collider, operated by the European Organization for Nuclear Research (CERN), located at the French-Swiss border near Geneva ...
(HL-LHC) project that will increase the luminosity by a factor of 10. LS2 ended in April 2022. The Long Shutdown 3 (LS3) in the 2020s will take place before the HL-LHC project is done.


Run 3: third operational run (2022)

LHC became operational again on 22 April 2022 with a new maximum beam energy of 6.8 TeV (13.6 TeV collision energy), which was first achieved on 25 April. It officially commenced its run 3 physics season on July 5, 2022. This round is expected to continue until 2026. In addition to a higher energy the LHC is expected to reach a higher luminosity, which is expected to increase even further with the upgrade to the HL-LHC after Run 3.


Timeline of operations


Findings and discoveries

An initial focus of research was to investigate the possible existence of the Higgs boson, a key part of the
Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
of physics which was 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 was 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.


First run (data taken 2009–2013)

The first physics results from the LHC, involving 284 collisions which took place in the ALICE detector, were reported on 15 December 2009. The results of the first proton–proton collisions at energies higher than Fermilab's Tevatron proton–antiproton collisions were published by the
CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color manag ...
collaboration in early February 2010, yielding greater-than-predicted charged-
hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the e ...
production. After the first year of data collection, the LHC experimental collaborations started to release their preliminary results concerning searches for new physics beyond the Standard Model in proton–proton collisions. No evidence of new particles was detected in the 2010 data. As a result, bounds were set on the allowed parameter space of various extensions of the Standard Model, such as models with
large extra dimensions In particle physics and string theory (M-theory), the ADD model, also known as the model with large extra dimensions (LED), is a model framework that attempts to solve the hierarchy problem. (''Why is the force of gravity so weak compared to the el ...
, constrained versions of the
Minimal Supersymmetric Standard Model The Minimal Supersymmetric Standard Model (MSSM) is an extension to the Standard Model that realizes supersymmetry. MSSM is the minimal supersymmetrical model as it considers only "the inimumnumber of new particle states and new interactions con ...
, and others. On 24 May 2011, it was reported that
quark–gluon plasma Quark–gluon plasma (QGP) or quark soup is an interacting localized assembly of quarks and gluons at thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasma'' signals that free color charges are allowed. In a ...
(the densest matter thought to exist besides
black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...
s) had been created in the LHC. Between July and August 2011, results of searches for the Higgs boson and for exotic particles, based on the data collected during the first half of the 2011 run, were presented in conferences in Grenoble and Mumbai. In the latter conference, it was reported that, despite hints of a Higgs signal in earlier data, ATLAS and CMS exclude with 95% confidence level (using the CLs method) the existence of a Higgs boson with the properties predicted by the Standard Model over most of the mass region between 145 and 466 GeV. The searches for new particles did not yield signals either, allowing to further constrain the parameter space of various extensions of the Standard Model, including its supersymmetric extensions. On 13 December 2011, CERN reported that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 115–130 GeV. Both the CMS and ATLAS detectors have also shown intensity peaks in the 124–125 GeV range, consistent with either background noise or the observation of the Higgs boson. On 22 December 2011, it was reported that a new composite particle had been observed, the χb (3P)
bottomonium In particle physics, quarkonium (from quark and -onium, pl. quarkonia) is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it both a neutral particle and its own antiparticle. Light quarks Light quarks ( up ...
state. On 4 July 2012, both the CMS and ATLAS teams announced the discovery of a boson in the mass region around 125–126 GeV, with a statistical significance at the level of 5 sigma each. This meets the formal level required to announce a new particle. The observed properties were consistent with the Higgs boson, but scientists were cautious as to whether it is formally identified as actually being the Higgs boson, pending further analysis. On 14 March 2013, CERN announced confirmation that the observed particle was indeed the predicted Higgs boson. On 8 November 2012, the LHCb team reported on an experiment seen as a "golden" test of
supersymmetry In a supersymmetric theory the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theories e ...
theories in physics, by measuring the very rare decay of the B_s
meson In particle physics, a meson ( or ) is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles ...
into two muons (B_s^0\rightarrow\mu^+\mu^-). The results, which match those predicted by the non-supersymmetrical
Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
rather than the predictions of many branches of supersymmetry, show the decays are less common than some forms of supersymmetry predict, though could still match the predictions of other versions of supersymmetry theory. The results as initially drafted are stated to be short of proof but at a relatively high 3.5 sigma level of significance. The result was later confirmed by the CMS collaboration. In August 2013, the LHCb team revealed an anomaly in the angular distribution of
B meson In particle physics, B mesons are mesons composed of a bottom antiquark and either an up (), down (), strange () or charm quark (). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark' ...
decay products which could not be predicted by the Standard Model; this anomaly had a statistical certainty of 4.5 sigma, just short of the 5 sigma needed to be officially recognized as a discovery. It is unknown what the cause of this anomaly would be, although the Z' boson has been suggested as a possible candidate. On 19 November 2014, the LHCb experiment announced the discovery of two new heavy subatomic particles, and . Both of them are baryons that are composed of one bottom, one down, and one strange quark. They are excited states of the bottom
Xi baryon The Xi baryons or ''cascade particles'' are a family of subatomic hadron particles which have the symbol and may have an electric charge () of +2 , +1 , 0, or −1 , where is the elementary charge. Like all conventional baryon ...
. The LHCb collaboration has observed multiple exotic hadrons, possibly pentaquarks or tetraquarks, in the Run 1 data. On 4 April 2014, the collaboration confirmed the existence of the tetraquark candidate
Z(4430) Z(4430) is a mesonic resonance discovered by the Belle experiment. It has a mass of . The resonant nature of the peak has been confirmed by the LHCb experiment with a significance of at least 13.9 σ. The particle is charged and is thought ...
with a significance of over 13.9 sigma. On 13 July 2015, results consistent with pentaquark states in the decay of
bottom Lambda baryon The lambda baryons (Λ) are a family of subatomic hadron particles containing one up quark, one down quark, and a third quark from a higher flavour generation, in a combination where the quantum wave function changes sign upon the flavour of an ...
s (Λ) were reported. On 28 June 2016, the collaboration announced four tetraquark-like particles decaying into a J/ψ and a φ meson, only one of which was well established before (X(4274), X(4500) and X(4700) and X(4140)). In December 2016, ATLAS presented a measurement of the W boson mass, researching the precision of analyses done at the Tevatron.


Second run (2015–2018)

At the conference EPS-HEP 2015 in July, the collaborations presented first cross-section measurements of several particles at the higher collision energy. On 15 December 2015, the
ATLAS An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
and
CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color manag ...
experiments both reported a number of preliminary results for Higgs physics,
supersymmetry In a supersymmetric theory the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theories e ...
(SUSY) searches and exotics searches using 13 TeV proton collision data. Both experiments saw a moderate excess around 750 GeV in the two-photon invariant mass spectrum, but the experiments did not confirm the existence of the hypothetical particle in an August 2016 report. In July 2017, many analyses based on the large dataset collected in 2016 were shown. The properties of the Higgs boson were studied in more detail and the precision of many other results was improved. As of March 2021, the LHC experiments have discovered 59 new hadrons in the data collected during the first two runs. On 5 July 2022 LHCb reported the discovery of a new type of
pentaquark A pentaquark is a human-made subatomic particle, consisting of four quarks and one antiquark bound together; they are not known to occur naturally, or exist outside of experiments specifically carried out to create them. As quarks have a baryo ...
made up of a charm quark and a charm antiquark and an up, a down and a strange quark, observed in an analysis of decays of charged B mesons.


Planned "high-luminosity" upgrade

After some years of running, any
particle physics Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
experiment typically begins to suffer from
diminishing returns In economics, diminishing returns are the decrease in marginal (incremental) output of a production process as the amount of a single factor of production is incrementally increased, holding all other factors of production equal ( ceteris parib ...
: as the key results reachable by the device begin to be completed, later years of operation discover proportionately less than earlier years. A common response is to upgrade the devices involved, typically in collision energy,
luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
, or improved detectors. In addition to a possible increase to 14 TeV collision energy, a luminosity upgrade of the LHC, called the High Luminosity Large Hadron Collider, started in June 2018 that will boost the accelerator's potential for new discoveries in physics, starting in 2027. The upgrade aims at increasing the luminosity of the machine by a factor of 10, up to 1035 cm−2s−1, providing a better chance to see rare processes and improving statistically marginal measurements.


Planned Future Circular Collider (FCC)

CERN has several preliminary designs for a Future Circular Collider (FCC) — which would be the most powerful particle smasher ever built — with different types of collider ranging in cost from around €9 billion (US$10.2 billion) to €21 billion. It is CERN’s opening bid in a priority-setting process called the European Strategy for Particle Physics Update, and will affect the field’s future well into the second half of the century. Not everyone is convinced that the FCC is a good investment. “There is no reason to think that there should be new physics in the energy regime that such a collider would reach,” says
Sabine Hossenfelder Sabine Hossenfelder (born 1976) is a German theoretical physicist, author, musician and YouTuber. She is currently employed as a research fellow at the Frankfurt Institute for Advanced Studies. She is the author of ''Lost in Math: How Beauty Le ...
, a theoretical physicist at the
Frankfurt Institute for Advanced Studies The Frankfurt Institute for Advanced Studies (FIAS) is a private-public institution for basic theoretical research in various areas of science focusing on interdisciplinary research. It is located in Frankfurt am Main, Germany, at its own home at ...
in Germany. Hossenfelder says that the large sums involved might be better spent on other types of huge facility. For example, she says that placing a major radio telescope on the far side of the Moon, or a gravitational-wave detector in orbit, would both be safer bets than the collider in terms of their return on science.


Safety of particle collisions

The experiments at the Large Hadron Collider sparked fears that the particle collisions might produce doomsday phenomena, involving the production of stable microscopic black holes or the creation of hypothetical particles called strangelets. Two CERN-commissioned safety reviews examined these concerns and concluded that the experiments at the LHC present no danger and that there is no reason for concern, a conclusion endorsed by the
American Physical Society The American Physical Society (APS) is a not-for-profit membership organization of professionals in physics and related disciplines, comprising nearly fifty divisions, sections, and other units. Its mission is the advancement and diffusion of k ...
. The reports also noted that the physical conditions and collision events that exist in the LHC and similar experiments occur naturally and routinely in the
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...
without hazardous consequences, including
ultra-high-energy cosmic ray In astroparticle physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray with an energy greater than 1 EeV (1018 electronvolts, approximately 0.16 joules), far beyond both the rest mass and energies typical of other cosmic ray parti ...
s observed to impact Earth with energies far higher than those in any human-made collider.


Popular culture

The Large Hadron Collider gained a considerable amount of attention from outside the scientific community and its progress is followed by most popular science media. The LHC has also inspired works of fiction including novels, TV series, video games and films. CERN employee
Katherine McAlpine Katherine "Kate" McAlpine (born 1985) is an American science journalist. In 2008, while working at CERN, McAlpine wrote, produced and performed in the YouTube video "Large Hadron Rap" under the pseudonym "alpinekat". As of September 2018, the v ...
's "Large Hadron Rap" surpassed 7 million
YouTube YouTube is a global online video platform, online video sharing and social media, social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by ...
views. The band
Les Horribles Cernettes ''Les Horribles Cernettes'' (, "The Horrible CERN Girls") was an all-female parody pop group, self-labelled "the one and only High Energy Rock Band", which was founded by employees of CERN and performed at CERN and other HEP-related events. Their ...
was founded by women from CERN. The name was chosen so to have the same initials as the LHC.
National Geographic Channel National Geographic (formerly National Geographic Channel; abbreviated and trademarked as Nat Geo or Nat Geo TV) is an American pay television television network, network and flagship (broadcasting), flagship channel owned by the National Geograp ...
's '' World's Toughest Fixes'', Season 2 (2010), Episode 6 "Atom Smasher" features the replacement of the last superconducting magnet section in the repair of the collider after the 2008 quench incident. The episode includes actual footage from the repair facility to the inside of the collider, and explanations of the function, engineering, and purpose of the LHC. The song "Munich" off of the 2012 studio album ''
Scars & Stories ''Scars & Stories'' is the third studio album by American alternative rock band The Fray. It was released on February 7, 2012. Background ''Scars & Stories'' was recorded beginning in March 2011, and concluded in July 2011. Unlike their debut alb ...
'' by
The Fray The Fray is an American rock band from Denver, Colorado, formed in 2002 by schoolmates Isaac Slade and Joe King. Their debut album, ''How to Save a Life'' released in 2005, was certified double platinum by the RIAA and platinum in Australia, ...
is inspired by the LHC. Lead singer
Isaac Slade Isaac Edward Slade (born May 26, 1981) is an American singer and musician; the former lead vocalist, main songwriter, pianist and co-founder of Colorado-based rock band The Fray. Early life Slade was born in Boulder, Colorado, and raised in t ...
said in an interview with ''
The Huffington Post ''HuffPost'' (formerly ''The Huffington Post'' until 2017 and sometimes abbreviated ''HuffPo'') is an American progressive news website, with localized and international editions. The site offers news, satire, blogs, and original content, and ...
'', "There's this large particle collider out in Switzerland that is kind of helping scientists peel back the curtain on what creates gravity and mass. Some very big questions are being raised, even some things that Einstein proposed, that have just been accepted for decades are starting to be challenged. They're looking for the God Particle, basically, the particle that holds it all together. That song is really just about the mystery of why we're all here and what's holding it all together, you know?" The Large Hadron Collider was the focus of the 2012 student film ''Decay'', with the movie being filmed on location in CERN's maintenance tunnels. The feature documentary ''
Particle Fever ''Particle Fever'' is a 2013 American documentary film tracking the first round of experiments at the Large Hadron Collider (LHC) near Geneva, Switzerland. The film follows the experimental physicists at the European Organization for Nuclear Rese ...
'' follows the experimental physicists at CERN who run the experiments, as well as the theoretical physicists who attempt to provide a conceptual framework for the LHC's results. It won the Sheffield International Doc/Fest in 2013.


Fiction

The novel ''
Angels & Demons ''Angels & Demons'' is a 2000 bestselling mystery- thriller novel written by American author Dan Brown and published by Pocket Books and then by Corgi Books. The novel introduces the character Robert Langdon, who recurs as the protagonist of B ...
'', by
Dan Brown Daniel Gerhard Brown (born June 22, 1964) is an American author best known for his thriller novels, including the Robert Langdon novels ''Angels & Demons'' (2000), '' The Da Vinci Code'' (2003), ''The Lost Symbol'' (2009), '' Inferno'' (2013), ...
, involves
antimatter In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter. Antimatter occurs in natural processes like cosmic ray collisions and some types of radioac ...
created at the LHC to be used in a
weapon A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
against the Vatican. In response, CERN published a "Fact or Fiction?" page discussing the accuracy of the book's portrayal of the LHC, CERN, and particle physics in general. The movie version of the book has footage filmed on-site at one of the experiments at the LHC; the director,
Ron Howard Ronald William Howard (born March 1, 1954) is an American director, producer, screenwriter, and actor. He first came to prominence as a child actor, guest-starring in several television series, including an episode of ''The Twilight Zone''. He ...
, met with CERN experts in an effort to make the science in the story more accurate. In the visual novel/
manga Manga (Japanese: 漫画 ) are comics or graphic novels originating from Japan. Most manga conform to a style developed in Japan in the late 19th century, and the form has a long prehistory in earlier Japanese art. The term ''manga'' is u ...
/anime-series '' Steins;Gate'', SERN (a deliberate misspelling of CERN) is an organization that uses the miniature black holes created from experiments in the LHC to master time travel and take over the world. It is also involved in mass surveillance through the " ECHELON" project and has connection with many mercenary groups worldwide, to avoid the creation of other time machines. The novel '' FlashForward'', by
Robert J. Sawyer Robert James Sawyer (born April 29, 1960) is a Canadian science fiction writer. He has had 24 novels published and his short fiction has appeared in ''Analog Science Fiction and Fact'', ''Amazing Stories'', '' On Spec'', ''Nature'', and numerou ...
, involves the search for the Higgs boson at the LHC. CERN published a "Science and Fiction" page interviewing Sawyer and physicists about the book and the
TV series A television show – or simply TV show – is any content produced for viewing on a television set which can be broadcast via over-the-air, satellite, or cable, excluding breaking news, advertisements, or trailers that are typically placed betw ...
based on it. In the ''
American Dad ''American Dad!'' is an American animated sitcom created by Seth MacFarlane, Mike Barker and Matt Weitzman for the Fox Broadcasting Company. Since 2014, the series has been airing new episodes on TBS. ''American Dad!'' is the first televisio ...
'' episode ''The 200'', Roger accidentally falls into the Large Hadron Collider, resulting in a huge explosion that creates two hundred clones of his multiple personas. In the American sitcom ''
The Big Bang Theory ''The Big Bang Theory'' is an American television sitcom created by Chuck Lorre and Bill Prady, both of whom served as executive producers on the series, along with Steven Molaro, all of whom also served as head writers. It premiered on C ...
'' episode "The Large Hadron Collision" (season 3 episode 15), Leonard is offered a chance to visit the Large Hadron Collider.


See also

*
List of accelerators in particle physics A list of particle accelerators used for particle physics experiments. Some early particle accelerators that more properly did nuclear physics, but existed prior to the separation of particle physics from that field, are also included. Although a m ...
* Accelerator projects **
Compact Linear Collider The Compact Linear Collider (CLIC) is a concept for a future linear particle accelerator that aims to explore the next energy frontier. CLIC would collide electrons with positrons and is currently the only mature option for a multi-TeV linear coll ...
**
Future Circular Collider The Future Circular Collider (FCC) is a proposed particle accelerator with an energy significantly above that of previous circular colliders, such as the Super Proton Synchrotron, the Tevatron, and the Large Hadron Collider (LHC). The FCC pro ...
** International Linear Collider **
Very Large Hadron Collider The Very Large Hadron Collider (VLHC) was a proposed future hadron collider planned to be located at Fermilab. The VLHC was planned to be located in a ring, using the Tevatron as an injector. The VLHC would run in two stages, initially the Stag ...


References


External links

*
Overview of the LHC at CERN's public webpage

CERN Courier magazine



LHC Portal
Web portal * Full documentation for design and construction of the LHC and its six detectors (2008). :Video * *
Animation of LHC in collision production mode (June 2015)
:News
Eight Things To Know As The Large Hadron Collider Breaks Energy Records
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