Large Hadron Collider

This article or section contains information about an expected future scientific facility.
It is likely to contain information of a speculative nature and the content may change as the facility approaches completion.

The accelerator chain of the
Large Hadron Collider (LHC)
LHC experiments
ATLASA Toroidal LHC ApparatuS
CMSCompact Muon Solenoid
ALICEA Large Ion Collider Experiment
TOTEMTotal Cross Section, Elastic
Scattering and Diffraction Dissociation
LHC preaccelerators
p and PbLinear accelerators
for protons and Lead
(not marked)Proton Synchrotron Booster
PSProton Synchrotron
SPSSuper Proton Synchrotron

The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland (). Currently under construction, the LHC is scheduled to begin operation in May 2008.[1] The LHC is expected to become the world's largest and highest energy particle accelerator. The LHC is being funded and built in collaboration with over two thousand physicists from thirty-four countries, universities and laboratories.

When activated, it is hoped that the collider will produce the elusive Higgs boson particle — often dubbed the God Particle — the observation of which could confirm the predictions and 'missing links' in the Standard Model of physics, and explain how other elementary particles acquire properties such as mass. The verification of the existence of the Higgs boson would be a significant step in the search for a Grand Unified Theory which seeks to unify the four fundamental forces: Electromagnetism, Strong Force, Weak Force, and Gravity. The higgs boson may help to explain why gravity is comparatively weak when contrasted with the other three fundamental forces.

Technical Design

The collider is contained in a 27 kilometre (17 mi) circumference tunnel located underground at a depth ranging from 50 to 175 metres.[2] The tunnel was formerly used to house the LEP, an electron-positron collider.

The three metre diameter, concrete-lined tunnel actually crosses the border between Switzerland and France at four points, although the majority of its length is inside France. The collider itself is located underground, with many surface buildings holding ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two pipes enclosed within superconducting magnets cooled by liquid helium, each pipe containing a proton beam. The two beams travel in opposite directions around the ring. Additional magnets are used to direct the beams to four intersection points where interactions between them will take place.

The protons will each have an energy of 7 TeV, giving a total collision energy of 14 TeV. It will take around ninety microseconds for an individual proton to travel once around the collider. Rather than continuous beams, the protons will be "bunched" together into approximately 2,800 bunches, so that interactions between the two beams will take place at discrete intervals never shorter than twenty-five nanoseconds apart. When the collider is first commissioned, it will be operated with fewer bunches, to give a bunch crossing interval of seventy-five nanoseconds. The number of bunches will later be increased to give a final bunch crossing interval of twenty-five nanoseconds.

Prior to being injected into the main accelerator, the particles are prepared through a series of systems that successively increase the particle energy levels. The first system is the linear accelerator Linac2 generating 50 MeV protons which feeds the Proton Synchrotron Booster (PSB). Protons are then injected at 1.4 GeV into the Proton Synchrotron (PS) at 26 GeV. The Low-Energy Injector Ring (LEIR) will be used as an ion storage and cooler unit. The Antiproton Decelerator (AD) will produce a beam of anti-protons at 2 GeV, after cooling them down from 3.57 GeV. Finally the Super Proton Synchrotron (SPS) can be used to increase the energy of protons up to 450 GeV.

Six detectors are being constructed at the LHC. They are located underground, in large caverns excavated at the LHC's intersection points. Two of them, ATLAS and CMS are large, "general purpose" particle detectors. The other four (LHCb, ALICE, TOTEM, and LHCf) are smaller and more specialized.

The LHC can also be used to collide heavy ions such as lead (Pb) with a collision energy of 1,150 TeV.

The size of the LHC constitutes an exceptional engineering challenge with unique safety issues. While running, the total energy stored in the magnets is 10 GJ, and in the beam, 725 MJ. Loss of only 10−7 of the beam is sufficient to quench a superconducting magnet, while the beam dump must absorb an energy equivalent to a typical air-dropped bomb. For comparison, 725 MJ is equivalent to the detonation energy of approximately 157 kg (347 pounds) of TNT, and 10 GJ is about 2.5 tons of TNT.


Enlarge picture
A Feynman diagram of one way the Higgs boson may be produced at the LHC. Here, two quarks each emit a W or Z boson which combine to make a neutral Higgs.
Enlarge picture
A simulated event in the CMS detector, featuring the appearance of the Higgs boson.
When in operation, about seven thousand scientists from eighty countries will have access to the LHC, the largest national contingent of seven hundred being from the United States. Physicists hope to use the collider to enhance their ability to answer the following questions:

LHC as an ion collider

The LHC physics program is mainly based on proton-proton collisions. However, shorter running periods, typically one month per year, with heavy-ion collisions are included in the programme. While lighter ions are considered as well, the baseline scheme deals with lead (Pb) ions.[4] This will allow an advancement in the experimental programme currently in progress at the Relativistic Heavy Ion Collider (RHIC).

LHC proposed upgrade

Enlarge picture
CMS detector for LHC
After some years of running, any particle physics experiment typically begins to suffer from diminishing returns. The way around the diminishing returns is to upgrade the experiment, either in energy or in luminosity.

A luminosity upgrade of the LHC, called the Super LHC, has been proposed,[5] to be made after ten years of LHC operation. The optimal path for the LHC luminosity upgrade includes an increase in the beam current (i.e., the number of protons in the beams) and the modification of the two high luminosity interaction regions, ATLAS and CMS. To achieve these increases, the energy of the beams at the point that they are injected into the (Super) LHC should also be increased to 1 TeV. This will require an upgrade of the full pre-injector system, the needed changes in the Super Proton Synchrotron being the most expensive.


The construction of LHC was originally approved in 1995 with a budget of 2600 million Swiss francs (currently about 1.7 billion euro), with another 210 million francs (€140 m) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (€300 m) in the accelerator, and 50 million francs (€30 m) for the experiments, along with a reduction in CERN's budget pushed the completion date out from 2005 to April 2007.[6] 180 million francs (€120 m) of the cost increase has been the superconducting magnets. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid.[7]


Main article: LHC@home
LHC@Home, a distributed computing project, was started to support the construction and calibration of the LHC. The project uses the BOINC platform to simulate how particles will travel in the tunnel. With this information, the scientists will be able to determine how the magnets should be calibrated to gain the most stable "orbit" of the beams in the ring.

Safety concerns and assurances

As with previous particle accelerators, people both inside and outside the physics community have voiced concern that the LHC might trigger one of several theoretical disasters capable of destroying the Earth or even the entire Universe. This has raised controversy as to whether any such risks outweigh the potential benefits of constructing and operating the LHC.

Though the standard model predicts that LHC energies are far too low to create black holes, some nonstandard theories lower the requirements, and predict that the LHC will create tiny black holes[8][9], with potentially devastating consequences. The primary cause for concern is that Hawking Radiation - a postulated means by which any such black holes would dissipate before becoming dangerous, remains entirely theoretical. In academia, the theory of Hawking Radiation is considered plausible, but there remains considerable question of whether it is correct.[10]

Other disaster scenarios typically involve the following theoretical events: CERN has pointed out that the probability of such events is extremely small. One argument for the safety of colliders such as the LHC states that if the Earth were in danger of any such fate, the Earth and Moon would have met that fate billions of years ago due to their constant bombardment from space by protons, other particles, and cosmic rays, which are millions of times more energetic than anything that could be produced by the LHC.[11]

Quantum calculations presented in the CERN report predict that:
  • Any black holes created by the LHC are not expected to be stable and will not accrete matter.
  • Any monopoles that could catalyse the decay of matter will quickly exit the Earth.[12]

Construction accidents and delays

On October 25, 2005, a technician was killed in the LHC tunnel when a crane load was accidentally dropped.[13][14]

On March 27, 2007, there was an incident during a pressure test involving one of the LHC's inner triplet magnet assemblies provided by Fermilab and KEK. No people were injured, but a cryogenic magnet support broke. 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.[15][16]

Repairing the broken magnet and reinforcing the eight identical copies used by LHC, in addition to a number of other small delays, caused a postponement of the planned November 26, 2007 startup date [17] to May 2008.[18]

See also

Notes and references

1. ^ New start-up schedule for world's most powerful particle accelerator
2. ^ Symmetry magazine, April 2005
3. ^ " the public presentations of the aspiration of particle physics we hear too often that the goal of the LHC or a linear collider is to check off the last missing particle of the standard model, this year’s Holy Grail of particle physics, the Higgs boson. The truth is much less boring than that! What we’re trying to accomplish is much more exciting, and asking what the world would have been like without the Higgs mechanism is a way of getting at that excitement." -Chris Quigg, Nature's Greatest Puzzles
4. ^ Ions for LHC
5. ^ PDF presentation of proposed LHC upgrade
6. ^ Maiani, Luciano (16 October 2001). LHC Cost Review to Completion. CERN. Retrieved on 2001-01-15.
7. ^ Feder, Toni (December 2001). "CERN Grapples with LHC Cost Hike". Physics Today 54 (12): 21. Retrieved on 2007-01-15. 
8. ^ American Institute of Physics Bulletin of Physics News, Number 558, September 26, 2001, by Phillip F. Schewe, Ben Stein, and James Riordon
9. ^ Dimopoulos, S. and Landsberg, G. Black Holes at the Large Hadron Collider. Phys. Rev. Lett. 87 (2001).
10. ^ Adam D. Helfer: General Relativity and Quantum Cosmology
11. ^ Tiny Black Holes - Physicist Dave Wark of Imperial College, London reporting for NOVA scienceNOW
12. ^ Blaizot, J.-P. et al. Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC. (PDF)
13. ^ Hewett, JoAnne (25 October 2005). Tragedy at CERN (Blog). Cosmic Variance. Retrieved on 2007-01-15. author and date indicate the beginning of the blog thread
14. ^ CERN (26 October 2005). Message from the Director-General (in English and French). Press release. Retrieved on 2007-01-15.
15. ^ LHC Magnet Test Failure
16. ^ Updates on LHC inner triplet failure
17. ^ The God Particle. Retrieved on 2007-05-22.
18. ^ CERN (2007-06-22). CERN announces new start-up schedule for world’s most powerful particle accelerator. Press release. Retrieved on 2007-07-01.

External links

ATLAS (A Toroidal LHC ApparatuS) is one of the six particle detector experiments (ALICE, ATLAS, CMS, TOTEM, LHCb, and LHCf) currently being constructed at the Large Hadron Collider (LHC), a new particle accelerator at the European Organization for
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Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors being (as of 2007) built on the proton-proton Large Hadron Collider (LHC) at CERN in Switzerland.
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The LHCb (standing for "Large Hadron Collider beauty") experiment is one of six particle physics detector experiments being constructed on the Large Hadron Collider accelerator at CERN.
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ALICE (A Large Ion Collider Experiment) is one of the six detector experiments being constructed at the Large Hadron Collider at CERN. It is optimized to study heavy ion collisions. Pb-Pb nuclei collisions will be studied at a centre of mass energy of 5.
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Total Cross Section, Elastic Scattering and Diffraction Dissociation (TOTEM) is one of the six detector experiments being constructed at the Large Hadron Collider at CERN in Switzerland. It shares intersection point I5 with the Compact Muon Solenoid.
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LHCf ("Large Hadron Collider forward") is a special-purpose LHC experiment for astroparticle (cosmic ray) physics, one of six being constructed on the Large Hadron Collider accelerator at CERN.
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linear particle accelerator (also called a LINAC) is an electrical device for the acceleration of subatomic particles. This sort of particle accelerator has many applications, from the generation of X-Rays in a hospital environment, to an injector into a higher energy
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The quark structure of the proton.
Composition: 2 up, 1 down
Family: Fermion
Group: Quark
Interaction: Gravity, Electromagnetic, Weak, Strong
Antiparticle: Antiproton
Discovered: Ernest Rutherford (1919)
Symbol: p+
Mass: 1.
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(Amphoteric oxide)
Electronegativity 2.33 (scale Pauling)
Ionization energies
(more) 1st: 715.6 kJmol−1
2nd: 1450.5 kJmol−1
3rd: 3081.
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The Proton Synchrotron Booster is the first and smallest proton circular accelerator in the CERN Large Hadron Collider injection complex. [1] It takes 50MeV protons from the linear accelerator Linac2 and accelerates them up to 1.
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The Proton Synchrotron (PS) was the first major particle accelerator at CERN, built as a 28 GeV proton accelerator in 1959. It takes the protons from the Proton Synchrotron Booster at 1.4GeV.
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The Super Proton Synchrotron (SPS) is a particle accelerator at CERN. Originally specified as a 300 GeV proton machine, the SPS was actually built to be capable of 400GeV, an operating energy it achieved on the official commissioning date of 17 June 1976.
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particle accelerator is a device that uses electric fields to propel electrically charged particles to high speeds and to contain them. An ordinary CRT television set is a simple form of accelerator. There are two basic types: linear (i.e.
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A collider is a type of a particle accelerator involving directed beams of particles.

In particle physics one gains knowledge about elementary particles by accelerating particles to very high kinetic energy and letting them impact on other particles.
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The European Organization for Nuclear Research (French: Organisation européenne pour la recherche nucléaire), commonly known as CERN (see Naming), pronounced
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Geneva (pronunciation /dʒənivə/; French: Genève /ʒənɛv/, German: Genf
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Unus pro omnibus, omnes pro uno (Latin) (traditional)[1]
"One for all, all for one"
"Swiss Psalm"
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university is an institution of higher education and research, which grants academic degrees at all levels (bachelor, master, and doctorate) in a variety of subjects. A university provides both tertiary and quaternary education.
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Higgs boson
Composition: Elementary particle
Family: Boson
Status: Hypothetical
Theorized: P. Higgs, F. Englert, R. Brout, G. S. Guralnik, C. R. Hagen, and T. W. B.
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Scientific method is a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. It is based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning,[1]
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Standard Model of particle physics is a theory which describes three of the four known fundamental interactions between the elementary particles that make up all matter. It is a quantum field theory developed between 1970 and 1973 which is consistent with both quantum mechanics and
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In particle physics, an elementary particle or fundamental particle is a not known to have substructure; that is, it is not known to be made up of smaller particles.
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relativistic mass is also used, this occasionally leads to confusion.

The invariant mass of an object (also known as the rest mass, intrinsic mass or proper mass) is an observer-independent quantity that is synonymous with mass.
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Higgs boson
Composition: Elementary particle
Family: Boson
Status: Hypothetical
Theorized: P. Higgs, F. Englert, R. Brout, G. S. Guralnik, C. R. Hagen, and T. W. B.
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Grand Unification, grand unified theory, or GUT is one of several very similar unified field theories or models in physics that unify what are considered three "fundamental" gauge symmetries: hypercharge, the weak force, and quantum chromodynamics (QCD).
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A fundamental interaction or fundamental force is a mechanism by which particles interact with each other, and which cannot be explained in terms of another interaction. Every observed physical phenomenon can be explained by these interactions.
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Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles.
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The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD).
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The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons.
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Gravitation is a natural phenomenon by which all objects with mass attract each other. In everyday life, gravitation is most familiar as the agency that endows objects with weight.
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