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Large Hadron Collider (LHC)

 Automatic translation  Automatic translation Updated June 01, 2013

Particles physics is primarily an experimental science. Observe tiny particles require very big microscopes!
The Large Hadron Collider is a gigantic scientific instrument built in the plain of Lake Geneva between Geneva and the Jura mountains straddling the Franco-Swiss border at a depth between 50 and 175 meters underground. CERN (European Council for Nuclear Research) has approved the construction of the LHC December 16, 1994 which was put into service September 10, 2008. In November 2000, the large electron-positron collider (LEP) gives way in the same tunnel, the LHC. The particle accelerator is a great 'toy' colossal with which hundreds of physicists study the smallest particles, the fundamental components of matter. The complex consists of a succession of energy accelerators still growing.


Each beam injected into the next machine, which takes over to bring the beam to an energy even higher, and so on.
It is the world's most powerful than the Tevatron at Fermilab in Chicago (United States).
The LHC is built in a tunnel 3 feet in diameter and 26.659 kilometers in circumference, will revolutionize our understanding of the Universe, the infinitely small to the infinitely large.
The LHC is a circular accelerator-proton collider.
The accelerating system of the LHC will bring energy to 7 TeV (1 teraelectron volt = 1.60217646 × 10-7 joules).

Image: The LHC is located in the plains around Lake Geneva. Virtual tour of the LHC here.

 LHC à la frontière franco-suisse

What is a collider?


Particle accelerators are instruments that use electric fields and / or magnetic bring electrically charged particles to very high speeds. In other words, they communicate energy particles.
The Collider is a machine where the beams circulating in opposite directions before colliding unlike other types of accelerators in which a beam collides with a stationary target.
These accelerators colliders are similar to synchrotrons because the particles travel along a circular path.
The two beams of particles launched at 99.9999991% the speed of light, will make 11 245 times around the accelerator per second, in reverse.


These particle beams run in two tubes where there is a combined UHV, inserted in the same superconducting magnet system cooled by liquid helium.

Image: This image shows the low curvature of the tunnel LHC 26.659 kilometers in circumference.
Credit: CERN

 Tunnel du LHC

Magnets at -271 ° C


The LHC's eight sectors are maintained at operating temperature of -271.2 ° C, 1.9 degrees above absolute zero.
One of the technical progress the most important of the late 20th century, has been mastering for the superconducting magnets and accelerating cavities.
Some metals cooled to near absolute zero (-273 ° C) then lose all electrical resistance and therefore there is more energy lost through heat dissipation, which allows them to move particles without loss power. These magnets cooled whose role is to bend the particle beams are used to direct these beams to four intersection points where interactions allow collisions between particles. The beams of subatomic particles to the family of hadrons (protons or lead ions) moving in the opposite direction then inside the circular accelerator, storing energy in each round.


If we collide two particles in opposite directions, each with energy E, energy in the center of mass is equal to 2 E.
At CERN, in Geneva, the Super Proton Synchrotron (SPS) reached energies of 450 GeV only if we can say compared to the 7 TeV LHC.
By bringing into collision the two beams at a speed approaching that of light and very high energies, the LHC recreate conditions that existed just after the Big Bang.
Teams of physicists and can analyze particles from these collisions.

Image: Power cryogenic LHC
Credit: CERN

 Alimentations cryogéniques du LHC - CERN

A new era of physics


There are many surveys about the outcome of these collisions. Physicists hope that this new era of physics brings their new data on the functioning of the universe. To understand the fundamental laws of Nature, physicists rely on the standard model describing remarkably particle physics. This model predicts the existence of a particle called boson de Higgs  The Higgs boson is a particle predicted by the famous "Standard Model" of particle physics. It is the missing link in this model. Indeed, this particle is supposed to explain the origin of mass of all particles in the Universe (including itself), but despite this role, it remains undiscovered because no experiment has so far observed conclusively. , whose detection is a priority objective of the LHC. Many theoretical arguments favor the existence of the so-called supersymmetry, which predicts that every known particle type has an alter ego called the super-partner. The detection of supersymmetry is the second issue of the LHC. Another issue is the identification of dark matter is thought to constitute much of the mass of the universe. String theory predicts the existence of extra dimensions beyond the three spatial dimensions we know.


Some collisions performed at the LHC could indirectly highlight, including the formation of microscopic black holes. If matter and antimatter existed in equal quantities during Big Bang were annihilated, what is the phenomenon called Baryogenesis, which has generated this tiny excess of matter over antimatter, which is now in space. The LHC could also find an answer to this question. Atomic nuclei are composed of protons and neutrons consist of basic entities called quarks. Quarks exist only in groups of 2 or 3 particles (3 in the case of neutrons and protons). At very high temperatures, quarks can exist in isolation, that is what the LHC will attempt to highlight.

Image: Control center LHC credit: CERN

 LHC centre de contrôle du CERN

Path of protons and lead ions


Each proton beam is composed of nearly 3,000 packets of particles, each containing 100 billion particles.
The particles are so small that the probability of collision is small. When the packets cross, it occurs only twenty collisions among 200 billion particles. However, packets intersect at a rate of about 30 million times per second, so the LHC generates up to 600 million collisions per second. A beam can travel for 10 hours, traveling more than 10 billion kilometers, twice the distance between Earth and Neptune. At a speed approaching that of light, a proton carries 11 245 revolutions per second in the LHC.
Here is the brief story of a proton accelerated by the accelerator complex at CERN: Hydrogen atoms are extracted from a bottle of ordinary hydrogen. Protons are obtained by tearing to hydrogen atoms in their electron orbit.
The protons pass from Linac2 in the injector of the Proton Synchrotron (PS Booster, PSB) at an energy of 50 MeV. The PSB accelerates to 1.4 GeV.
The beam is then injected into the Proton Synchrotron (PS), where its energy is raised to 25 eV.
Then the protons are sent in the Super Proton Synchrotron (SPS), where they are accelerated to 450 GeV. Finally, they are transferred to the LHC (in the sense of clockwise and vice versa, with a refill time of 4 min 20 s per ring), where they are accelerated for 20 minutes to be brought to the nominal energy of 7 TeV. In normal operation, the beams circulate for several hours in the pipes of the LHC.
The protons in the LHC come in packets, which are prepared in smaller machines.


Image: The LHC is built in a tunnel of 3 meters in diameter and 26.659 kilometers in circumference.
At a speed approaching that of light, a proton carries 11 245 revolutions per second in the LHC. CERN source

History of lead ions


The accelerator complex accelerates not only protons but also lead ions. The lead ions are produced from a sample of lead of extreme purity heated to a temperature of about 500 ° C.
The ions thus produced are highly variable loads, with a maximum around PB29 +. These selected ions are then accelerated to an energy of 4.2 MeV / u (energy per nucleon) before pass through a sheet of carbon that the "peeling" and turns most into Pb54 +.
Once accumulated, Pb54+ ions are accelerated to 72 MeV/u in LEIR (ring of low energy ions), then transferred to the PS.


It accelerates the beam to bring it to 5.9 GeV/u and sends it in the SPS, after having been through a second sheet that the "peeler" completely, producing PB82 +. The SPS is the beam to 177 GeV/u and then injected into the LHC, which accelerates it to 2.76 TeV/u.

Video: Large hadron Collider (CERN source).


Alice, 12 DVD of data per minute


The particle detector is Alice in France, it was formally approved in February 1997 and moved into his cave in June 2001.
Around one of four collision points of LHC is the particle detector Alice (A Large Ion Collider Experiment) which studies nuclear matter in a state of extreme temperature and density, 'soup' of quarks (the ultimate constituents atomic nuclei) and gluon (gluon transmits the strong interaction between quarks) that would have existed a few microseconds after Big Bang.
The detector must be able to separate the many particles produced in each lead-lead collision.
Some collisions can generate tens of thousands of tracks and it is therefore necessary to have a very high computing power for their reconstruction.


Alice will produce about 12 DVDs of data per minute. The data stream produced by the ALICE experiment will be the most important of all LHC experiments.
It will manage and process these data.

Image: Alice is 16 m in height and 26 m in length, Credit: CERN

 Alice LHC 

Atlas and the Higgs boson


The particle detector Atlas is in Switzerland.
The agreement for the design of this magnet toroid, the largest magnetic coil in the world, was signed in 1996 and Atlas was built in February 1999.
The excavation of the largest experimental hall in the world (35 m wide, 55 meters long and 40 m high) was completed in June 2002 to accommodate the 6,000-ton Atlas detector in November 2003.
Around one of four collision points of the LHC is a giant particle detector Atlas (A Toroidal LHC Apparatus) that could discover new elementary particles like the Higgs boson, a particle vainly sought to date, to find super symmetric particles or access to extra dimensions of space.
Atlas was designed as a versatile detector, which seeks to identify and accurately measure the characteristics (energy, speed and direction) of particles produced during collisions.


High as a six-storey building, this giant machine is located 100 meters underground, to be at the intersection of two beams of protons from the accelerator. His cave could contain the nave of Notre Dame de Paris.

Image: Atlas is 35 m wide, 55 meters long and 40 m high, Credit: CERN

 Atlas LHC 

CMS to the 5th dimension and more


The CMS detector is located in France. On January 22, 2008, 1430 tonnes of the last element of CMS is lowered into the cavern marking the final commissioning of CMS.
On one of the four collision points of LHC to Cessy in France, is the detector CMS (Compact Muon Solenoid) could discover new elementary particles like the Higgs boson which has never been observed and vainly sought to date, find super symmetric particles or highlight additional dimensions of space. CMS superconducting solenoid has the largest and most powerful ever built.
The magnetic field intensity outstanding (4 Tesla, or 100 000 times the Earth's magnetic field) is to deflect charged particles.
CMS's mission is to recognize with accuracy and finesse each type of particle produced and select interesting events.


CMS 21.5 meters long and has a diameter of 15 meters and a mass of 12 500 tonnes is housed in a cave 27 meters wide and 53 meters long and 24 meters high.
It was dug in the wet layers, it has been frozen by injecting brine at -23 ° C and liquid nitrogen at -80 ° C.

Image: CMS is 21.5 m and a diameter of 15 m and a mass of 12 500 tonnes, Credit: CERN


LHCb detector "beauty"


The LHCb detector is located in France. The assembly began in January 2003 with the descent of two coils of the magnet in the underground experimental area.
Around one of four collision points of LHC is the LHCb (Large Hadron Collider beauty experiment) who studied the matter-antimatter asymmetry in tracking specific particles containing a quark. The ultimate goal is to better understand why the universe consists entirely of material, while at birth matter and antimatter were present in equal parts.
It must achieve the best possible detection of particles 'beautiful' (containing a b quark) and their decay products.
The particles so-called "beauty" have a long lifetime of wide range of particles as they travel a few millimeters before decaying.


The LHCb experiment is distinguished by its ability to reconstruct precisely where these particles disintegrate.

Image: LHCb detector beauty in his cave.
Credit: CERN

 LHCb le détecteur de beauté

Record figures for the LHC


120 megawatt,
This machine consumes about 120 MW (230 MW for the whole CERN), which corresponds roughly to the power consumed by all households in the Canton of Geneva.
Assuming that the accelerator operates 270 days per year (the machine stops during the winter), the annual energy consumption of the LHC in 2009 will reach about 800 000 MWh.


This figure includes the consumption of the machine, its infrastructure and experience.
The total annual cost to operate the LHC will be about 19 million euros.
CERN is mainly powered from the French company EDF while Swiss companies EOS and SIG Swiss provide electricity in case of shortage French side.


9 teslas ,
The bending magnets, the dipoles include two magnets for both vacuum tubes where the protons move in opposite directions.
These magnets, 15 meters long and about 35 tons, produced in their heart a magnetic field of 9 tesla, about 200 000 times the Earth's magnetic field.


700 m3 of liquid helium
The magnets are first cooled to 80 K using 12 500 tonnes of liquid nitrogen, then to 1.9 K with 700 m3 of liquid helium. In April 2007, one eighth of the ring is cooled by liquid helium at 1.9 K (-271.2 ° C), colder than outer space. Sector 7-8 3.3 km long and is the largest superconducting installation in the world.

 LHC helium liquide

Image: The liquid helium cryogenic fluid, cooling the superconducting magnets of the LHC at -271 ° C.

1.1 gigabytes per second,
A record of data on backup tapes is defeated in May 2003 with a transfer rate of 1.1 gigabytes per second for several hours.
This equates to record a movie on DVD every four seconds.
The data produced by year reaching, 15 peta bytes.

NB: 1 peta = 1015 or 1 000 000 000 000 000 bytes.


2.38 gigabits per second,
A record of data transfer is beaten over 10 000 km between CERN and California, with a throughput of 2.38 gigabits per second for over an hour.
This is equivalent to sending 200 DVD films in an hour.

Table: quantities and units used in information science, and names and symbols for these quantities and units. The standard is published by the International Electrotechnical Commission (IEC) and is part of the group of standards called ISO/IEC 80000, published jointly by the IEC and the International Organization for Standardization (ISO).

Multiples of bits Metric Value
1 bit bit 1
103 Kbit kilobit 10241
106 Mbit megabit 10242
109 Gbit gigabit 10243
1012 Tbit terabit 10244
1015 Petabit petabit 10245
1018 Ebit exabit 10246
1021 Zbit zettabit 10247
1024 Ybit yottabit 10248

14 TeV energy created
The highest energies ever attained by man, 7 TeV proton beam of nominal.
The collision energy of 14 TeV, is seven times higher than the most powerful accelerator in the world, Fermilab's Tevatron in Batavia, Illinois west of Chicago, USA.


NB: 1 teraelectron volt = 1,60217646 × 10-7 joules.

Image: The Tevatron ring and main injector.

 Tevatron Fermilab

The ultravid,
To avoid collisions with gas molecules present in the accelerator, the beams of particles travel in a cavity as empty as interplanetary space, the so-called ultra. Three systems of the LHC vacuum team.
The internal pressure of the LHC is 10-13 atmosphere.
The pressure in the tubes of the LHC beam will be approximately ten times smaller than the Moon.


More than 9000 physicists,
The LHC has the largest concentration of researchers through the collaboration of its member states: Austria, Belgium, Denmark, Finland, France, Greece, Hungary, Italy, Norway, Netherlands, Poland, Portugal, Republic Slovak, Czech Republic, United Kingdom, Sweden and Switzerland. The Russian Federation, Israel, Turkey, Yugoslavia, the European Commission and UNESCO have observer status.

 LHC chercheurs

And now...


The accelerators have become increasingly powerful, more expensive and therefore less numerous: 2 in Europe, 2 in the United States and 1 in Japan. The LHC project of 3 billion euros is a successful European technology that will address the outstanding issues of the Standard Model (Higgs boson, super symmetry, dark matter, extra dimensions of matter, black holes, Baryogenesis,...) .
Answering these questions requires a large theoretical effort but also experimental, so the physics community looks forward to the first results of the Large Hadron Collider, which will necessarily require new concepts.
This orgy of power and resources deployed, is the price of a working tool in the service of physicists who can thus be tested in extreme conditions, the modern theories on particles and antiparticles.


Image: The commissioning of the LHC, which took place September 10, 2008, was disappointing for unsuspecting viewers could see a small white dot on the video screen (bottom left-cons below). More photos on the site Boston: here

 LHC mise en service

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