Cern Lhc Guide

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CERNaqLHCthe guide

LINAC 2

Gran Sasso

North Area

LINAC 3Ions

East Area

TI2TI8

TT41TT40

CTF3

TT2

TT10

TT60

e

ALICE

ATLAS

LHCb

CMS

CNGS

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neutrons

pp

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This is a collection o acts and gures about theLarge Hadron Collider (LHC) in the orm o questionsand answers. Questions are grouped into sections,and answers are oten two-tier, with more details inthe second level. Please note that when speakingabout particle collisions in the accelerator, the wordinteraction is a synonym o collision.

This guide is regularly updated. For the latest version,please visit:

http://multimedia-gallery.web.cern.ch/multimedia-gallery/Brochures.aspx


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Contentsaq

LHCthe guide

Physics preamble 1

The LHC in general 15

The machine 27

Detectors 37

Environment 47

10 ascinating actsabout the LHC 52

Appendix 1 53

Appendix 2 54


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Simulation o a lead-lead collision in the ALICE detector.


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1

Physics preamble

Powers o ten

The powers o ten are commonly used in physics and inormationtechnology. They are practical shorthand or very large or very smallnumbers.

Power o ten Number Symbol

1012

109

106

103

102

101

100101

102

103

106

109

1012

1015

0.0000000000010.000000001

0.0000010.0010.010.1

1101001000

1 000 0001 000 000 000

1 000 000 000 0001 000 000 000 000 000

p (pico)n (nano)m (micro)m (milli)

k (kilo)M (mega)G (giga)T (tera)P (peta)

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Atom

Electron

Nucleon

Nucleus

u

u d

Molecule

Proton

Quarks

Matter

Inside the atom

Particle physics studies the tinest objects o Nature. Looking intothe very small and undamental, it also looks very ar back intotime, just a ew moments ater the Big Bang. Here are a ew exam-ples o dimensions particle physicists deal with:

Atom: 10-10 mNucleus: 10-14 mQuarks: < 10-19 m

I the protons and the neu-trons were 10 cm across,then the quarks and elec-trons would be less than 0.1mm in size and the entireatom would be about 10 kmacross. More than 99.99% othe atom is empty space.

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Energy units in physics

Energy has many units in physics: joules, calories, and kilowatthours are all units o energy used in dierent contexts. Only the

joule is an International System (SI) unit, but all o them are relat-ed by conversion actors. In particle physics, the unit that is mostrequently used or energy is the electronvolt (eV) and its deriva-tives keV (103 eV), MeV (106 eV), GeV (109 eV) and TeV (1012 eV).The electronvolt is a convenient unit because, in absolute terms,the energies that particle physicists deal with are very small. I wetake the LHC as an example, the total collision energy is 14 TeV,

making it the most powerul particle accelerator in the world. Still,i we convert this into joules, we obtain:

14 x 1012 x 1.602 x 1019 = 22.4 x 107 joules.

This is a very small amount o energy i compared, or example, tothe energy o an object weighing 1 kg and alling rom a height o1 m, that is: 9.8 joules = 6.1 x 1019 electronvolts.

The denition o the electronvolt comes rom the simple in-sight that a single electron accelerated by a potential dierenceo 1 volt will have a discreet amount o energy, E=qV joules,where q is the charge on the electron in coulombs and V is the

potential dierence in volts. Hence 1 eV = (1.602 x 1019 C)x (1 V) = 1.602 x 1019 J.

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Energy and speed o a particle

No particle can move with speeds aster than the speed o light ina vacuum; however, there is no limit to the energy a particle canattain. In high-energy accelerators, particles normally travel veryclose to the speed o light. In these conditions, as the energy in-creases, the increase in speed is minimal. As an example, particlesin the LHC move at 0.999997828 times the speed o light at injec-tion (energy = 450 GeV) and 0.999999991 times the speed o lightat top energy (energy = 7000 GeV). Thereore, particle physicistsdo not generally think about speed, but rather about a particles

energy.

The classical Newtonian relationship between speed and kineticenergy (K = (1/2)mv2) only holds or speeds much lower thanthe speed o light. For particles moving close to the speed olight we need to use Einsteins equation rom special relativ-ity K = (g1)mc2 where c is the velocity o light (299 792 458m/s), andgis related to speed via g= 1/(1b2); b= v/c and

m = mass o particle at rest.

E

4 mc2

3 mc2

2 mc

2

mc2

0.2 c 0.4 c 0.6 c 0.8 c c

velocity v

E = mc2

kineticenergy

properor restenergy

E = mc2

energy

Re: http://www.phys.unsw.edu.au/einsteinlight/jw/module5_equations.htm

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Kinetic energyo a proton (K)

Speed (%c) Accelerator

50 MeV

1.4 GeV25 GeV450 GeV7 TeV

31.4

91.699.93

99.999899.9999991

Linac 2

PS BoosterPSSPSLHC

Relationship between kinetic energy and speed o a proton in the CERNmachines. The rest mass o the proton is 0.938 GeV/c2

Energy and mass

Energy and mass are two sides o the same coin. Mass can transorminto energy and vice versa in accordance with Einsteins amousequation (E=mc2). At the LHC this transormation happens at each

collision. Also, because o this equivalence, mass and energy can bemeasured with the same units. At the scale o particle physics theseare the electronvolt and its multiples (see Energy units in physics).

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The Standard Model

The Standard Model is a collection o theories that embodies allo our current understanding o undamental particles and orces.According to the theory, which is supported by a great deal o ex-perimental evidence, quarks are the building blocks o matter, andorces act through carrier particles exchanged between the particleso matter. Forces also dier in their strength. The ollowing picturessummarize the Standard Models basic points.

Although the Standard Model is a very powerul theory, some othe phenomena recently observed such as dark matter andthe absence o antimatter in the Universe remain unexplainedand can not be accounted or in the model. Read more aboutthis on page 22.

Mathematical representation o the Standard Model o particle physics.

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ElectronTogether with the nucleus, itmakes up the atom

Electron neutrinoParticle with no electriccharge, and very smallmass; billions y throughyour body every second

MuonA heavier relative o theelectron; it lives or two-millionths o a second

Muon neutrinoCreated along withmuons when someparticles decay

TauHeavier still; it isextremely unstable.It was discoveredin 1975

Tau neutrinoDiscovered in2000

UpHas an electric charge oplus two-thirds;protons contain two,neutrons contain one

DownHas an electric charge ominus one-third; protonscontain one, neutronscontain two

CharmA heavier relative

o the up;ound in 1974

StrangeA heavier relative

o the down.

TopHeavier still;ound in 1995

BottomHeavier still; measuringbottom quarks is animportant test oelectroweak theory

LEPTONS

QUARKS

Makeupm

atter

Makeupmatter

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Felt by: quarks

Carrier: gluons

Felt by: quarks andcharged leptons

Carrier: photons

AssociatedphenomenaIt holds electronsto nuclei in atoms,binds atoms into

molecules, and isresponsible or theproperties o solids,

liquids and gases.

STRONG FORCE

ELECTROMAGNETIC FORCE

u

u d

Associated

phenomenaThe strong orcebinds quarks togeth-er to make protonsand neutrons (andother particles).

It also binds protonsand neutrons in nu-clei, where it over-comes the enormous

electrical repulsionbetween protons.

Gluons

Photons

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AssociatedphenomenaGravity makes applesall to the ground.It is an attrac-

tive orce. On anastronomical scale itbinds matter in plan-ets and stars, andholds stars together

in galaxies.

Associated

phenomenaThe weak orceunderlies naturalradioactivity, orexample in the

Earth beneath oureet. It is alsoessential or thenuclear reactionsin the centres o

stars like the Sun,where hydrogenis converted intohelium.

Felt by: quarks and

leptonsCarrier: intermediatevector bosons

WEAK FORCE

GRAVITATION

Felt by: all particleswith mass

Carrier: Graviton

Graviton

Boson

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Back to the Big Bang

The energy density and temperature that will be made available inthe collisions at the LHC are similar to those that existed a ew mo-ments ater the Big Bang. In this way physicists hope to discoverhow the Universe evolved.

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The CERN accelerator complex

The accelerator complex at CERN is a succession o machines withincreasingly higher energies. Each machine injects the beam intothe next one, which takes over to bring the beam to an even higherenergy, and so on. In the LHCthe last element o this chaineach particle beam is accelerated up to the record energy o 7 TeV.In addition, most o the other accelerators in the chain have theirown experimental halls, where the beams are used or experimentsat lower energies.

The brie story o a proton accelerated through the acceleratorcomplex at CERN is as ollows:

} Hydrogen atoms are taken rom a bottle containing hydrogen.We get protons by stripping orbiting electrons rom hydrogenatoms.

} Protons are injected into the PS Booster (PSB) at an energy o50 MeV rom Linac2.

The booster accelerates them to 1.4 GeV. The beam is then edto the Proton Synchrotron (PS) where it is accelerated to 25 GeV.Protons are then sent to the Super Proton Synchrotron (SPS)where they are accelerated to 450 GeV. They are nally trans-

erred to the LHC (both in a clockwise and an anticlockwise di-rection, the lling time is 420 per LHC ring) where they are ac-celerated or 20 minutes to their nominal energy o 7 TeV. Beamswill circulate or many hours inside the LHC beam pipes undernormal operating conditions.

Protons arrive at the LHC in bunches, which are prepared in the smaller machines. For a complete scheme o lling, magneticelds and particle currents in the accelerator chain, have a lookat Appendix 1 and 2.

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In addition to accelerating protons, the accelerator complex alsoaccelerates lead ions.

Lead ions are produced rom a highly puried lead sample heated

to a temperature o about 500C. The lead vapour is ionizedby an electron current. Many dierent charge states are pro-duced with a maximum around Pb29+. These ions are selectedand accelerated to 4.2 MeV/u (energy per nucleon) beore pass-ing through a carbon oil, which strips most o them to Pb54+.The Pb54+ beam is accumulated, then accelerated to 72 MeV/uin the Low Energy Ion Ring (LEIR), which transers them to thePS. The PS accelerates the beam to 5.9 GeV/u and sends it to theSPS ater rst passing it through a second oil where it is ully

stripped to Pb82+. The SPS accelerates it to 177 GeV/u then sendsit to the LHC, which accelerates it to 2.76 TeV/u.

LINAC 2

Gran Sasso

North Area

LINAC 3Ions

East Area

TI2TI8

TT41TT40

CTF3

TT2

TT10

TT60

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ALICE

ATLAS

LHCb

CMS

CNGS

neutrinos

neutrons

pp

SPS

ISOLDEBOOSTER

AD

LEIR

n-ToF

LHC

PS50 MeV

1.4 GeV

25 GeV

450 GeV

7 TeV

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The LHC tunnel and aerial layout.


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What does LHC stand or?

LHC stands or Large Hadron Collider. Large due to its size

(approximately 27 km in circumerence), Hadron because it accel-erates protons or ions, which are hadrons, and Colliderbecausethese particles orm two beams travelling in opposite directions,which collide at our points where the two rings o the machineintersect.

Hadrons (rom the Greek adros meaning bulky) are particlescomposed o quarks. The protons and neutrons that atomic nuclei

are made o belong to this amily. On the other hand, leptons areparticles that are not made o quarks. Electrons and muons areexamples o leptons (rom the Greek leptos meaning thin).

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When was it designed?

Back in the early 1980s, while the Large Electron-Positron (LEP)collider was being designed and built, groups at CERN were alreadybusy looking at the long-term uture. Ater many years o work onthe technical aspects and physics requirements o such a machine,their dreams came to ruition in December 1994 when CERNs gov-erning body, the CERN Council, voted to approve the constructiono the LHC. The green light or the project was given under the con-dition that the new accelerator be built within a constant budgetand on the understanding that any non-Member State contributions

would be used to speed up and improve the project. Initially, thebudgetary constraints implied that the LHC was to be conceived asa 2-stage project. However, ollowing contributions rom Japan, theUSA, India and other non-Member States, Council voted in 1995 toallow the project to proceed in a single phase. Between 1996 and1998, our experimentsALICE, ATLAS, CMS and LHCbreceivedofcial approval and construction work commenced on the oursites. Since then, two smaller experiments have joined the quest:

TOTEM, installed next to CMS, and LHC, next to ATLAS (see experi-ments, page 37).

For more inormation about the LHC milestones, see:http://www.cern.ch/LHC-Milestones/

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How much does it cost?

The cost or the machine alone is about 5 billion CHF (about 3 bil-lion Euro). The total project cost breaks down roughly as ollows:

Construction costs(MCHF)

Personnel Materials Total

LHC machine andareas*)

1224 3756 4980

CERN share to detec-tors

869 493 1362

LHC computing (CERNshare)

85 83 168

Total 2178 4332 6510

*) This includes: Machine R & D and injectors, tests and pre-operation.

The experimental collaborations are individual entities, unded in-dependently rom CERN. CERN is a member o each experiment, andcontributes to the material budget o CMS and LHCb at the 20%level, 16% or ALICE and 14% or ATLAS. TOTEM is a much smallerexperiment, with a total material cost o about 6 million CHF, owhich CERN provides 30% o the budget.

NB: 1 billion = 1 thousand million.

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Why large?

The size o an accelerator is related to the maximum energy obtain-able. In the case o a collider or storage ring, this is a unction othe radius o the machine and the strength o the dipole magneticfeld that keeps particles in their orbits. The LHC re-uses the 27-kmcircumerence tunnel that was built or the previous big accelerator,LEP. The LHC uses some o the most powerul dipoles and radio-requency cavities in existence. The size o the tunnel, magnets,cavities and other essential elements o the machine, represent themain constraints that determine the design energy o 7 TeV perproton beam.

Why collider?

A collider (that is a machine where counter-circulating beams col-

lide) has a big advantage over other kinds o accelerator where abeam collides with a stationary target. When two beams collide, theenergy o the collision is the sum o the energies o the two beams.A beam o the same energy that hits a fxed target would produce acollision o much less energy.

The energy available (or example, to make new particles) inboth cases is the centre-o-mass energy. In the rst case it is

simply the sum o the energies o the two colliding particles(E = Ebeam1 + Ebeam2), whereas in the second, it is proportionalto the square root o the energy o the particle hitting the target(E Ebeam).

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Why hadrons?

The LHC will accelerate two beams o particles o the same kind,either protons or lead ions, which are hadrons. An accelerator canonly accelerate certain kinds o particle: frstly they need to becharged (as the beams are manipulated by electromagnetic devicesthat can only inuence charged particles), and secondly, except inspecial cases, they need not to decay. This limits the number oparticles that can practically be accelerated to electrons, protons,and ions, plus all their antiparticles.

In a circular accelerator, such as the LHC, heavy particles such asprotons (protons are around 2000 times more massive than elec-trons) have a much lower energy loss per turn through synchrotronradiation than light particles such as electrons. Thereore, in circu-lar accelerators, to obtain the highest-energy collisions it is moreeective to accelerate massive particles.

Synchrotron radiation is the name given to the radiation thatoccurs when charged particles are accelerated in a curved path ororbit. This kind o radiation represents an energy loss or parti-cles, which in turn means that more energy must be provided bythe accelerator to keep the beam energy constant.

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Why is the LHC built underground?

The LHC re-uses the tunnel that was built or CERNs previous bigaccelerator, LEP, dismantled in 2000. The underground tunnel wasthe best solution to house a 27-km circumerence machine becauseit is cheaper to excavate a tunnel rather than acquire the land tobuild at the surace and the impact on the landscape is reduced toa minimum. In addition, the Earths crust provides good shieldingor radiation.

The tunnel was built at a mean depth o 100 m, due to geologicalconsiderations (again translating into cost) and at a slight gradiento 1.4%. Its depth varies between 175 m (under the Jura) and 50 m(towards Lake Geneva).

The tunnel has a slope or reasons o cost. At the time when itwas built or hosting LEP, the construction o the vertical shatswas very costly. Thereore, the length o the tunnel that liesunder the Jura was minimized. Other constraints involved in the

positioning o the tunnel were:

} it was essential to have a depth o at least 5 m below the topo the molasse (green sandstone) stratum

} the tunnel had to pass in the vicinity o the pilot tunnel,constructed to test excavation techniques

} it had to link to the SPS. This meant that there was only onedegree o reedom (tilt). The angle was obtained by minimising

the depth o the shats.

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What is the collision energy at the LHC and what is sospecial about it?

Each proton beam ying around the LHC will have an energy o7 TeV, so when two protons collide the collision energy will be14 TeV. Lead ions have many protons, and together they give aneven greater energy: the lead-ion beams will have a collision en-ergy o 1150 TeV. Both collision energies have never been reachedbeore in a lab.

Energy concentration is what makes particle collisions so special.

When you clap your hands you probably do a collision at an energyhigher than protons at the LHC, but much less concentrated! Nowthink o what you would do i you were to put a needle in oneo your hands. You would certainly slow your hands down as youclapped!

In absolute terms, these energies, i compared to the energieswe deal with everyday, are not impressive. In act, 1 TeV is about

the energy o motion o a fying mosquito. What makes the LHCso extraordinary is that it squeezes energy into a space about amillion million times smaller than a mosquito.

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What are the main goals o the LHC?

Our current understanding o the Universe is incomplete. TheStandard Model o particles and orces (see page 6) summarizesour present knowledge o particle physics. The Standard Model hasbeen tested by various experiments and it has proven particularlysuccessul in anticipating the existence o previously undiscoveredparticles. However, it leaves many unsolved questions, which theLHC will help to answer.

} The Standard Model does not explain the origin o mass, nor why

some particles are very heavy while others have no mass at all.The answer may be the so-called Higgs mechanism. Accordingto the theory o the Higgs mechanism, the whole o space isflled with a Higgs feld, and by interacting with this feld,particles acquire their masses. Particles that interact intenselywith the Higgs feld are heavy, while those that have eeble in-teractions are light. The Higgs feld has at least one new particleassociated with it, the Higgs boson. I such a particle exists,experiments at the LHC will be able to detect it.

} The Standard Model does not oer aunifed description o all theundamental orces, as it remains difcult to construct a theory ogravity similar to those or the other orces. Supersymmetry atheory that hypothesises the existence o more massive partnerso the standard particles we know could acilitate the uni-fcation o undamental orces. I supersymmetry is right, thenthe lightest supersymmetric particles should be ound at theLHC.

} Cosmological and astrophysical observations have shown thatall o the visible matter accounts or only 4% o the Universe.The search is open or particles or phenomena responsible ordark matter (23%) and dark energy (73%). A very popular ideais that dark matter is made o neutral but still undiscov-ered supersymmetric particles.

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The rst hint o the existence o dark matter came in 1933,when astronomical observations and calculations o gravitationaleects revealed that there must be more stu present in the

Universe than we could account or by sight. Researchers now be-lieve that the gravitational eect o dark matter makes galaxies

spin aster than expected, and that its gravitational eld devi-ates the light o objects behind it. Measurements o these eects

show the existence o dark matter, and can be used to estimateits density even though we cannot directly observe it.

Dark energy is a orm o energy that appears to be associatedwith the vacuum in space, and makes up approximately 70% o

the Universe. Dark energy is homogenously distributed through-out the Universe and in time. In other words, its eect is not di-luted as the Universe expands. The even distribution means thatdark energy does not have any local gravitational eects, butrather a global eect on the Universe as a whole. This leads toa repulsive orce, which tends to accelerate the expansion o theUniverse. The rate o expansion and its acceleration can be meas-ured by experiments using the Hubble law. These measurements,together with other scientic data, have conrmed the existence

o dark energy and have been used to estimate its quantity.

} The LHC will also help us to investigate the mystery o antimat-ter.Matter and antimatter must have been produced in the sameamounts at the time o the Big Bang, but rom what we haveobserved so ar, our Universe is made only o matter. Why? TheLHC could help to provide an answer.

It was once thought that antimatter was a perect refectiono matter that i you replaced matter with antimatter andlooked at the result as i in a mirror, you would not be able totell the dierence. We now know that the refection is imperect,and this could have led to the matter-antimatter imbalance inour Universe.

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The strongest limits on the amount o antimatter in the Universecome rom the analysis o the diuse cosmic gamma-rays andthe inhomogeneities o the cosmic microwave background (CMB).

Assuming that ater the Big Bang, the Universe separated some-how into dierent domains where either matter or antimatterwas dominant, it is evident that at the boundaries there shouldbe annihilations, producing cosmic (gamma) rays. Taking intoaccount annihilation cross-sections, distance, and cosmic red-

shits, this leads to a prediction o the amount o diuse gammaradiation that should arrive on Earth. The ree parameter in themodel is the size o the domains. Comparing with the observed

gamma-ray fux, this leads to an exclusion o any domain size

below 3.7 giga light years, which is not so ar away rom theentire Universe. Another limit comes rom analyzing the inhomo-

geneities in the CMB antimatter domains (at any size) wouldcause heating o domain boundaries and show up in the CMBas density fuctuations. The observed value o ~10-5 sets strongboundaries to the amount o antimatter in the early Universe.

} In addition to the studies o protonproton collisions, heavy-ioncollisions at the LHC will provide a window onto the state omatter that would have existed in the early Universe, calledquark-gluon plasma. When heavy ions collide at high energiesthey orm or an instant a freball o hot, dense matter thatcan be studied by the experiments.

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According to the current theories, the Universe, born rom theBig Bang, went through a stage during which matter existed as a

sort o extremely hot, dense soup called quark-gluon plasma

(QGP) composed o the elementary building blocks o matter.As the Universe cooled, the quarks became trapped into com-posite particles such as protons and neutrons. This phenomenonis called the connement o quarks. The LHC is able to repro-duce the QGP by accelerating and colliding together two beamso heavy ions. In the collisions, the temperature will exceed100 000 times that o the centre o the Sun. In these conditions,the quarks are reed again and the detectors can observe and

study the primordial soup, thus probing the basic properties o

the particles and how they aggregate to orm ordinary matter.

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Octan

t8

Octant

7

Octa

nt6

Octant5O

cta

nt4

Octan

t

3

Octant2

Octant1

Beam dumpArrt des faisceaux

Injection

Inje

ctio

n

Beam cleaningNettoyage des faisceaux

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LHCb

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What are the important parameters or an accelerator?

We build accelerators to study processes whose probability varieswith collision energy, and which are oten rare. This means that orphysicists the most important parameters are the beam energy andthe number o interesting collisions. More specifcally, in a collidersuch as the LHC the probability or a particular process varies withwhat is known as the luminosity a quantity that depends on thenumber o particles in each bunch, the requency o complete turnsaround the ring, the number o bunches and the beam cross-sec-tion. In brie, we need to squeeze the maximum number o particlesinto the smallest amount o space around the interaction region.

What are the main ingredients o an accelerator?

In an accelerator, particles circulate in a vacuum tube and are ma-nipulated using electromagnetic devices: dipole magnets keep theparticles in their nearly circular orbits, quadrupole magnets ocusthe beam, and accelerating cavities are electromagnetic resonatorsthat accelerate particles and then keep them at a constant energyby compensating or energy losses.

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Vacuum in the LHC: the LHC has the particularity o having not one,but three vacuum systems:

- insulation vacuum or cryomagnets

- insulation vacuum or the helium distribution line

- beam vacuum

The beam vacuum pressure will be 1013 atm (ultrahigh vacuum),because we want to avoid collisions with gas molecules. The largestvolume to be pumped in the LHC is the insulation vacuum or thecryomagnets (~ 9000 m3 like pumping down the central nave o acathedral!)

Magnets: There is a large variety o magnets in the LHC, includingdipoles, quadrupoles, sextupoles, octupoles, decapoles, etc. giving atotal o about 9600 magnets. Each type o magnet contributes to op-timizing a particles trajectory. Most o the correction magnets are em-bedded in the cold mass o the main dipoles and quadrupoles. The LHCmagnets have either a twin aperture (or example, the main dipoles),or a single aperture (or example, some o the insertion quadrupoles).

Insertion quadrupoles are special magnets used to ocus the beamdown to the smallest possible size at the collision points, thereby

maximizing the chance o two protons smashing head-on into eachother. The biggest magnets are the 1232 dipoles.

Cavities: The main role o the LHC cavities is to keep the 2808 protonbunches tightly bunched to ensure high luminosity at the collision

points and hence, maximize the number o collisions. They also deliverradiorequency (RF) power to the beam during acceleration to the topenergy. Superconducting cavities with small energy losses and large

stored energy are the best solution. The LHC will use eight cavities

per beam, each delivering 2 MV (an accelerating eld o 5 MV/m)at 400 MHz. The cavities will operate at 4.5 K (-268.7C)(the LHCmagnets will use superfuid helium at 1.9 K or -271.3C). For the LHCthey will be grouped in ours in cryomodules, with two cryomodules perbeam, and installed in a long straight section o the machine wherethe transverse interbeam distance will be increased rom the normal195 mm to 420 mm.

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The ollowing table lists the important parameters or the LHC.

Quantity number

CircumerenceDipole operating temperatureNumber o magnetsNumber o main dipolesNumber o main quadrupolesNumber o RF cavitiesNominal energy, protonsNominal energy, ionsPeak magnetic dipole feldMin. distance between bunchesDesign luminosityNo. o bunches per proton beamNo. o protons per bunch (at start)Number o turns per secondNumber o collisions per second

26 659 m1.9 K (-271.3C)

95931232392

8 per beam7 TeV

2.76 TeV/u (*)8.33 T~7 m

1034 cm2 s1

28081.1 x 1011

11 245600 million

(*) Energy per nucleon

Will the LHC beam energy be inuenced by the Moon aswas the case or the LEP accelerator?

At the LHC, beam energy will be inuenced by the Moon in muchthe same way as at LEP. The absolute collision energy is not as criti-cal an issue or the LHC experiments as it was at LEP, but the tidalvariations will have to be taken into account when the beams areinjected into the collider.

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The phenomenon o tides in the ocean due to the infuence o theMoon (and to a lesser extent that o the Sun) is well known. Theycause the level o water on the edge o the sea to rise and all

with a cycle o some 12 hours. The ground is also subject to theeect o lunar attraction because the rocks that make it up areelastic. At the new Moon and when the Moon is ull, the Earthscrust rises by some 25 cm in the Geneva area under the eect othese ground tides. This movement causes a variation o 1 mmin the circumerence o the LHC (or a total circumerence o26.6 km) and this produces changes in beam energy. Thus, phys-icists must take the Moon into account in their measurements.

What is so special about the LHC dipoles?

The dipoles o the LHC represented the most important technologicalchallenge or the LHC design. In a proton accelerator like the LHC,the maximum energy that can be achieved is directly proportional

to the strength o the dipole feld, given a specifc accelerationcircumerence. At the LHC the dipole magnets are superconductingelectromagnets and able to provide the very high feld o 8.3 T overtheir length. No practical solution could have been designed usingwarm magnets instead o superconducting ones.

The LHC dipoles use niobium-titanium (NbTi) cables, which becomesuperconducting below a temperature o 10 K (263.2C), that is,they conduct electricity without resistance. In act, the LHC willoperate at 1.9 K (271.3C), which is even lower than the tem-perature o outer space (2.7 K or 270.5C). A current o 11 850 Aows in the dipoles, to create the high magnetic feld o 8.33 T,required to bend the 7 TeV beams around the 27-km ring o theLHC. I the magnets were made to work at a temperature o 4.5 K(-268.7C ), they would produce a magnetic feld o only 6.8 T. Forcomparison, the total maximum current or an average amily houseis about 100 A.

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The temperature o 1.9 K (271.3C) is reached by pumping super-uid helium into the magnet systems. Each dipole is 15 m long andweighs around 35 t.

The magnet coils or the LHC are wound rom a cable consistingo up to 36 twisted 15-mm strands, each strand being made upin turn o 6000-9000 individual laments, each lament havinga diameter as small as 7 micrometres (or comparison, a humanhair is about 50 micrometres thick). The 27-km circumerence othe LHC calls or some 7600 km o cable, corresponding to about270 000 km o strand enough to circle the Earth six timesat the Equator. I all the component laments were unravelled,

they would stretch to the Sun and back ve times with enoughlet over or a ew trips to the Moon (see Fact 2, page 52).

What is so special about the cryogenic system?

The LHC is the largest cryogenic system in the world and one othe coldest places on Earth. Such a cold temperature is required tooperate the magnets that keep the protons on course (see question:what is so special about the LHC dipoles?). To maintain its 27-kmring (4700 tonnes o material in each o the eight sectors) at su-peruid helium temperature (1.9 K, 271.3C), the LHCs cryogenicsystem will have to supply an unprecedented total rerigerationcapacity some 150 kW or rerigerators at 4.5 K and 20 kW orthose at 1.9 K. The layout or the rerigeration system is based on

fve cryogenic islands. Each island must distribute the coolantand carry kilowatts o rerigeration over a long distance. The wholecooling process will take a ew weeks.

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The rerigeration process happens in three phases:

1) cool down to 4.5 K (-268.7C),

2) flling with liquid helium o the magnet cold masses

3) fnal cool down to 1.9 K (-271.3C).

The frst phase happens in two steps: frst helium is cooled in thererigerators heat exchangers to 80 K by using about 10 000 t oliquid nitrogen. Then rerigerator turbines bring the helium tem-perature down to 4.5 K (-268.7C), ready or injection into themagnets cold masses. Once the magnets are flled, the rerig-

eration units bring the temperature down to 1.9 K (-271.3C).In total, about 120 t o helium will be needed, o which about90 t will be used in the magnets and the rest in the pipes and re-rigerator units.

Liquid nitrogen is never directly injected into the LHC to avoid anypossible source o asphyxiation in the underground tunnel.

Why superuid helium?

The choice o the operating temperature or the LHC has as much todo with the super properties o helium as with those o the super-conducting niobium-titanium alloy in the magnet coils. At atmos-pheric pressure helium gas liquefes at around 4.2 K (269.0 C),but when it is cooled urther it undergoes a second phase changeat about 2.17 K (271.0 C) to its superuid state. Among manyremarkable properties, superuid helium has a very high thermalconductivity, which makes it the coolant o choice or the rerigera-tion and stabilization o large superconducting systems (see alsoquestion : What is so special about the cryogenic system?).

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In all, LHC cryogenics will need some 40 000 leak-tight pipejunctions, and 120 t o helium will be required by the LHC ma-chine to keep the magnets at their operating temperature o

1.9 K. 60% o the helium will be in the magnet cold masses whilethe remaining 40% will be shared between the distribution sys-tem and the rerigerators. During normal operation most o thehelium will circulate in closed rerigeration loops. Nevertheless,each year, a certain percentage o the inventory could be lostdue to acility stops, leakage to the atmosphere, conditioning oinstallations and operational problems.

Why do we talk about bunches?

The protons o the LHC circulate around the ring in well-defnedbunches. The bunch structure o a modern accelerator is a directconsequence o the radio requency (RF) acceleration scheme.Protons can only be accelerated when the RF feld has the cor-rect orientation when particles pass through an accelerating cavity,which happens at well specifed moments during an RF cycle.

In the LHC, under nominal operating conditions, each pro-ton beam has 2808 bunches, with each bunch containing about1011 protons.

The bunch size is not constant around the ring. Each bunch, as itcirculates around the LHC, gets squeezed and expandedor in-stance it gets squeezed as much as possible around the interactionpoints to increase the probability o a collision. Bunches o parti-cles measure a ew centimetres long and a millimetre wide whenthey are ar rom a collision point. However, as they approach thecollision points, they are squeezed to about 16 mm (a human hair isabout 50 mm thick) to allow or a greater chance o proton-protoncollisions. Increasing the number o bunches is one o the ways toincrease luminosity in a machine. At ull luminosity the LHC uses

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ATLAS

CMS

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How do we see particles?

For each collision, the physicists goal is to count, track and char-acterize all the dierent particles that were produced in order toreconstruct the process in ull. Just the track o the particle givesmuch useul inormation, especially i the detector is placed insidea magnetic feld: the charge o the particle, or instance, will beobvious since particles with positive electric charge will bend oneway and those with negative charge will bend the opposite way.Also the momentum o the particle (the quantity o motion, whichis equal to the product o the mass and the velocity) can be de-termined: very high momentum particles travel in almost straightlines, low momentum particles make tight spirals.

Photons

Electrons or positrons

Muons

Pions or protons

Neutrons

Tracking

chamber

Electromagnetic

calorimeter

Hadron

calorimeter

Muon

detector

aq

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What are the detectors at the LHC?

There are six experiments installed at the LHC: A Large Ion ColliderExperiment (ALICE), ATLAS, the Compact Muon Solenoid (CMS), theLarge Hadron Collider beauty (LHCb) experiment, the Large HadronCollider orward (LHC) experiment and the TOTal Elastic and dirac-tive cross section Measurement (TOTEM) experiment. ALICE, ATLAS,CMS and LHCb are installed in our huge underground caverns builtaround the our collision points o the LHC beams. TOTEM will be in-stalled close to the CMS interaction point and LHC will be installednear ATLAS.

What is ALICE?

ALICE is a detector specialized in analysing lead-ion collisions. Itwill study the properties o quark-gluon plasma, a state o matter

where quarks and gluons, under conditions o very high tempera-tures and densities, are no longer confned inside hadrons. Such astate o matter probably existed just ater the Big Bang, beore par-ticles such as protons and neutrons were ormed. The internationalcollaboration includes more than 1500 members rom 104 institutesin 31 countries (July 2007).

Size

WeightDesign

Material costLocation

26 m long, 16 m high, 16 m wide

10 000 tonnescentral barrel plus single arm orwardmuon spectrometer115 MCHFSt Genis-Pouilly, France.

For more inormation, visit: http://aliceino.cern.ch/Public/

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What is ATLAS?

ATLAS is a general-purpose detector designed to cover the widestpossible range o physics at the LHC, rom the search or the Higgsboson to supersymmetry (SUSY) and extra dimensions. The maineature o the ATLAS detector is its enormous doughnut-shapedmagnet system. This consists o eight 25-m long superconductingmagnet coils, arranged to orm a cylinder around the beam pipethrough the centre o the detector. ATLAS is the largest-volumecollider-detector ever constructed. The collaboration consists omore than 1900 members rom 164 institutes in 35 countries (April2007).

SizeWeightDesignMaterial costLocation

46 m long, 25 m high and 25 m wide7000 tonnesbarrel plus end caps540 MCHFMeyrin, Switzerland.

For more inormation, visit: http://atlas.ch/

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What is CMS?

CMS is a general-purpose detector with the same physics goalsas ATLAS, but dierent technical solutions and design. It is builtaround a huge superconducting solenoid. This takes the orm o acylindrical coil o superconducting cable that will generate a mag-netic feld o 4 T, about 100 000 times that o the Earth. More than2000 people work or CMS, rom 181 institutes in 38 countries (May2007).

SizeWeightDesignMaterial costLocation

21 m long, 15 high m and 15 m wide.12 500 tonnesbarrel plus end caps500 MCHFCessy, France.

For more inormation, visit: http://cmsino.cern.ch/outreach/

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What is LHCb?

LHCb specializes in the study o the slight asymmetry between mat-ter and antimatter present in interactions o B-particles (particlescontaining the b quark). Understanding it should prove invaluablein answering the question: Why is our Universe made o the matterwe observe? Instead o surrounding the entire collision point withan enclosed detector, the LHCb experiment uses a series o sub-detectors to detect mainly orward particles. The frst sub-detectoris built around the collision point, the next ones stand one behindthe other, over a length o 20 m. The LHCb collaboration has morethan 650 members rom 47 institutes in 14 countries (May 2007).

SizeWeightDesign


21m long, 10m high and 13m wide5600 tonnesorward spectrometer with planardetectors75 MCHFFerney-Voltaire, France.

For more inormation, visit: http://lhcb.web.cern.ch/lhcb/

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What is LHC?

LHC is a small experiment that will measure particles produced veryclose to the direction o the beams in the proton-proton collisionsat the LHC. The motivation is to test models used to estimate theprimary energy o the ultra high-energy cosmic rays. It will havedetectors 140 m rom the ATLAS collision point. The collaborationhas 21 members rom 10 institutes in 6 countries (May 2007).

Size

WeightLocation

two detectors, each measures 30 cm long,

10 cm high, 10 cm wide40 kg eachMeyrin, Switzerland (near ATLAS).

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What is TOTEM?

TOTEM will measure the eective size or cross-section o the protonat LHC. To do this TOTEM must be able to detect particles producedvery close to the LHC beams. It will include detectors housed inspecially designed vacuum chambers called Roman pots, which areconnected to the beam pipes in the LHC. Eight Roman pots will beplaced in pairs at our locations near the collision point o the CMSexperiment. TOTEM has more than 70 members rom 10 institutes in7 countries (May 2007).

SizeWeightDesign


440 m long, 5 m high and 5 m wide20 tonnesroman pot and GEM detectors andcathode strip chambers6.5 MCHFCessy, France (near CMS)

For more inormation visit: http://totem.web.cern.ch/Totem/

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What dictates the general shape o the LHC particledetectors?

A modern general-purpose high-energy physics detector, such asATLAS or CMS, needs to be hermetic, so that there is only a smallprobability o a (detectable) particle escaping undetected througha region that is not instrumented. For engineering convenience,most modern detectors at particle colliders like the LHC adopt thebarrel plus endcaps design where a cylindrical detector covers thecentral region and two at circular endcaps cover the angles closeto the beam (the orward region). ALICE and LHCb have asymmetric

shapes as they ocus on more specifc areas o physics.

What are the main components o a detector?

The purpose o the large detectors installed at the LHC is to identiythe secondary particles produced in collisions, and to measure theirpositions in space, their charges, speed, mass and energy. To dothis, the detectors have many layers or sub-detectors that eachhave a particular role in the reconstruction o collisions. A magnetsystem completes the design. Its unction is to separate the dier-ent particles according to their charge and to allow the measure-ment o their momentum a physical quantity linked to the massand speed o the particle.

There are two important categories o subdetector:

uTracking devices reveal the tracks o electrically charged parti-cles through the trails they leave by ionizing matter. In a mag-netic feld they can be used to measure the curvature o a par-ticles trajectory and hence the particles momentum. This canhelp in identiying the particle. Most modern tracking devicesdo not make the tracks directly visible. Instead, they produceelectrical signals that can be recorded as computer data. A com-puter program reconstructs the patterns o tracks recorded.

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Two specialized types o tracking devices are vertex detectors andmuon chambers. Vertex detectors are located close to the inter-action point (primary vertex); muon chambers are located at theouter layers o a detector assembly because muons are the onlycharged particles able to travel through metres o dense material.

There are two main techniques used to build tracking devices:

} Gaseous chambers, where the medium ionized is a gas andthe ions or electrons are collected on electrodes usually inthe orm o wires or pads under strong electric elds. In dritchambers, the position o the track is ound by timing howlong the electrons take to reach an anode wire, measured rom

the moment that the charged particle passed through. Thisresults in higher spatial resolution or wider wire separation:drit cells are typically several centimetres across, giving a

spatial resolution o 50-100 mm. In a time projection chamberthe drit volume is much larger, up to 2 m or more, and the

sense wires are arranged on one end ace.

} Semiconductor detectors, where the particle creates electronsand holes as it passes through a reverse-biased semiconductor,usually silicon. The devices are subdivided into strips or pixels;typical resolution is 10 mm.

uCalorimeters are devices that measure the energy o particles bystopping them and measuring the amount o energy released.There are two main types o calorimeter: electromagnetic (ECAL)and hadronic (HCAL). They use dierent materials dependingon which type o particle they are stopping. The ECAL gener-ally ully absorbs electrons and photons, which interact readily

through the electromagnetic orce. Strongly interacting parti-cles (hadrons), such as protons and pions, may begin to loseenergy in the ECAL but will be stopped in the HCAL. Muons (andneutrinos) will pass through both layers. Calorimeters providethe main way to identiy neutral particles such as photons andneutrons; although they are not visible in tracking devices, theyare revealed by the energy they deposit in the calorimeters.

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Calorimeters typically consist o layers o passive or absorbinghigh density material (lead or instance) interleaved with layerso active medium such as solid lead-glass or liquid argon.

Detectors also oten have sub-detectors measuring the speed ocharged particles, an essential actor or particle identifcation.

There are two important methods or measuring the velocity oparticles:

} Cherenkov radiation: when a charged particle traverses amedium above a certain velocity, it emits photons at a specicangle that depends on the velocity. When combined with ameasurement o the momentum o the particle the velocitycan be used to determine the mass and hence to identiy the

particle. For Cherenkov emission to occur the particle must betravelling aster than the speed o light in the medium.

} Transition radiation: when a relativistic charged particletraverses an inhomogeneous medium, in particular the boundarybetween materials with dierent electrical properties, it emitsradiation more or less in proportion to its energy. This allows

particle types to be distinguished rom each other.

What will be the Higgs boson production rate at the LHC?

Although the particle collision rate at the LHC will be very high, the

production rate o the Higgs will be so small that physicists expectto have enough statistics only ater about 2-3 years o data-taking.The Higgs boson production rate strongly depends on the theoreti-cal model and calculations used to evaluate it. Under good condi-tions, there is expected to be about one every ew hours per ex-periment. The same applies to supersymmetric particles. Physicistsexpect to have the frst meaningul results in about one year odata-taking at ull luminosity.

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What is the expected data ow rom the LHCexperiments?

The LHC experiments represent about 150 million sensors deliveringdata 40 million times per second. Ater fltering there will be about100 collisions o interest per second.

The data ow rom all our experiments will be about 700 MB/s,that is around 15 000 000 GB (=15 PB) per year, corresponding toa stack o CDs about 20 km tall each year. This enormous amount

o data will be accessed and analysed by thousands o scientistsaround the world. The mission o the LHC Computing Grid is to buildand maintain a data storage and analysis inrastructure or the en-tire high-energy physics community that will use the LHC.

} ATLAS will produce about 320 MB/s

}CMS will produce about 300 MB/s

} LHCb will produce about 50 MB/s

} ALICE will produce about 100 MB/sduring proton-proton running and1.25 GB/s during heavy-ion running Concorde

(15 km)

Mont-Blanc(4.8 km)

CD stack with1 year LHC data!

(~ 20 Km)

Sounding balloon(30 km)

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Environment

What is the LHC power consumption?

It is around 120 MW (230 MW or all CERN), which corresponds moreor less to the power consumption or households in the Canton(State) o Geneva. Assuming an average o 270 working days or theaccelerator (the machine will not work in the winter period), theestimated yearly energy consumption o the LHC in 2009 is about800 000 MWh. This includes site base load and the experiments.The total yearly cost or running the LHC is thereore, about 19million Euros. CERN is supplied mainly by the French company EDF(Swiss companies EOS and SIG are used only in case o shortagerom France).

A large raction o the LHC electrical consumption will be to keepthe superconducting magnet system at the operating tempera-tures (1.8 and 4.2 K) depending on the magnets. Thanks to the

superconducting technology employed or its magnets, the nomi-nal consumption o the LHC is not much higher than that o theSuper Proton Synchrotron (SPS), even though the LHC is muchlarger and higher in energy.

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Are the LHC collisions dangerous?

The LHC can achieve energies that no other particle acceleratorshave reached beore. The energy o its particle collisions has pre-viously only been ound in Nature. And it is only by using such apowerul machine that physicists can probe deeper into the keymysteries o the Universe. Some people have expressed concernsabout the saety o whatever may be created in high-energy particlecollisions. However there are no reasons or concern.

} Unprecedented energy collisions? On Earth only! Accelerators onlyrecreate the natural phenomena o cosmic rays under control-led laboratory conditions. Cosmic rays are particles produced inouter space in events such as supernovae or the ormation oblack holes, during which they can be accelerated to energiesar exceeding those o the LHC. Cosmic rays travel throughoutthe Universe, and have been bombarding the Earths atmospherecontinually since its ormation 4.5 billion years ago. Despitethe impressive power o the LHC in comparison with other ac-celerators, the energies produced in its collisions are greatly

exceeded by those ound in some cosmic rays. Since the muchhigher-energy collisions provided by nature or billions o yearshave not harmed the Earth, there is no reason to think that anyphenomenon produced by the LHC will do so. Cosmic rays alsocollide with the Moon, Jupiter, the Sun and other astronomicalbodies. The total number o these collisions is huge comparedto what is expected at the LHC. The act that planets and starsremain intact strengthens our confdence that LHC collisions aresae. The LHCs energy, although powerul or an accelerator, is

modest by natures standards.

} Mini big bangs? Although the energy concentration (or density)in the particle collisions at the LHC is very high, in absoluteterms the energy involved is very low compared to the ener-gies we deal with every day or with the energies involved inthe collisions o cosmic rays. However, at the very small scaleso the proton beam, this energy concentration reproduces theenergy density that existed just a ew moments ater the Big

Bangthat is why collisions at the LHC are sometimes reerredto as mini big bangs.

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} Black holes? Massive black holes are created in the Universe bythe collapse o massive stars, which contain enormous amountso gravitational energy that pulls in surrounding matter. Thegravitational pull o a black hole is related to the amount omatter or energy it contains the less there is, the weakerthe pull. Some physicists suggest that microscopic black holescould be produced in the collisions at the LHC. However, thesewould only be created with the energies o the colliding parti-cles (equivalent to the energies o mosquitoes), so no micro-scopic black holes produced inside the LHC could generate astrong enough gravitational orce to pull in surrounding matter.I the LHC can produce microscopic black holes, cosmic rays o

much higher energies would already have produced many more.Since the Earth is still here, there is no reason to believe thatcollisions inside the LHC are harmul.

Black holes lose matter through the emission o energy via aprocess discovered by Stephen Hawking. Any black hole that can-not attract matter, such as those that might be produced at theLHC, will shrink, evaporate and disappear. The smaller the blackhole, the aster it vanishes. I microscopic black holes were to be

ound at the LHC, they would exist only or a feeting moment.They would be so short-lived that the only way they could bedetected would be by detecting the products o their decay.

} Strangelets? Strangelets are hypothetical small pieces o matterwhose existence has never been proven. They would be made ostrange quarks heavier and unstable relatives o the basicquarks that make up stable matter. Even i strangelets do ex-ist, they would be unstable. Furthermore, their electromagneticcharge would repel normal matter, and instead o combiningwith stable substances they would simply decay. I strangeletswere produced at the LHC, they would not wreak havoc.I theyexist, they would already have been created by high-energy cos-mic rays, with no harmul consequences.

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} Radiation? Radiation is unavoidable at particle accelerators like theLHC. The particle collisions that allow us to study the origin o mat-ter also generate radiation. CERN uses active and passive protectionmeans, radiation monitors and various procedures to ensure that ra-diation exposure to the sta and the surrounding population is aslow as possible and well below the international regulatory limits.For comparison, note that natural radioactivity due to cosmicrays and natural environmental radioactivity is about 2400 Sv/year in Switzerland. A round trip EuropeLos Angeles ight accountsor about 100 Sv. The LHC tunnel is housed 100 m underground,so deep that both stray radiation generated during operation andresidual radioactivity will not be detected at the surace. Air will

be pumped out o the tunnel and fltered. Studies have shown thatradioactivity released in the air will contribute to a dose to memberso the public o no more than 10 Sv/year.

CERNs guidelines or the protection o the environment and per-sonnel comply with the Swiss and French National Legislations andwith the European Council Directive 96/29/EURATOM. In both theSwiss and French legislations under no circumstances can proes-

sional activities lead to an eective dose o more than 20 mSv per

year or occupationally exposed persons and more than 1 mSv peryear or persons not occupationally exposed and or members othe public.

What are the rules regarding access to the LHC?

Outside beam operation, the larger part o the LHC tunnel will be

only weakly radioactive, the majority o the residual dose rates be-ing concentrated in specifc parts o the machine, such as the dumpcaverns where the ull beam is absorbed at the end o each physicsperiod and the regions where beams are collimated.

Only a selection o authorized technical people will be able to accessthe LHC tunnel. A specialized radiation protection technician will ac-cess it frst and measure the dose rate at the requested interventionplace, to assess when, and or how long, the intervention can takeplace.

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What is the helium consumption at the LHC?

The exact amount o helium loss during operation o the LHC isnot yet known. The actual value will depend on many actors, suchas how oten there are magnet quenches, power cuts and otherproblems. What is well known is the amount o helium that willbe needed to cool down the LHC and fll it or frst operation. Thisamount is around 120 t.

What happens i the beam becomes unstable?

The energy stored in the LHC beams is unprecedented, threaten-ing to damage accelerator equipment in case o uncontrolled beamloss, so everything is done to ensure that this never happens. Saeoperation o the LHC requires correct operation o several systems:collimators and beam absorbers, a beam dumping system, beam

monitoring, beam interlocks, and quench protection systems. I thebeam becomes unstable the beam loss sensors will detect it andwithin three revolutions (< 0.3 ms) a set o magnets will extractthe beam rom the LHC. The beam will then travel through a specialtunnel to the beam stop block, which is the only item in the LHCthat can withstand the impact o the ull beam. The core o the stopblock is made o a stack o various graphite plates with dierentdensities.

The total energy in each beam at maximum energy is about350 MJ, which is about as energetic as a 400 t train, like theFrench TGV, travelling at 150 km/h. This is enough energy tomelt around 500 kg o copper. The total energy stored in the LHCmagnets is some 30 times higher (11 GJ).

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10 Fascinating Factsabout the LHC

Fact 1) When the 27-km long circular tunnel was excavated, between LakeGeneva and the Jura mountain range, the two ends met up to within 1 cm.

Fact 2) Each o the 6000-9000 superconducting laments o niobiumti-tanium in the cable produced or the LHC is about 0.007 mm thick, about10 times thinner than a normal human hair. I you added all the lamentstogether they would stretch to the Sun and back six times with enough letover or about 150 trips to the Moon.

Fact 3) All protons accelerated at CERN are obtained rom standard hydro-gen. Although proton beams at the LHC are very intense, only 2 nanogramso hydrogen*) are accelerated each day. Thereore, it would take the LHCabout 1 million years to accelerate 1 gram o hydrogen.

Fact 4) The central part o the LHC will be the worlds largest ridge. At atemperature colder than deep outer space, it will contain iron, steel and theall important superconducting coils.

Fact 5 ) The pressure in the beam pipes o the LHC will be about ten timeslower than on the Moon. This is an ultrahigh vacuum.

Fact 6) Protons at ull energy in the LHC will be travelling at 0.999999991times the speed o light. Each proton will go round the 27 km ring more than11 000 times a second.

Fact 7)At ull energy, each o the two proton beams in the LHC will have atotal energy equivalent to a 400 t train (like the French TGV) travelling at150 km/h. This is enough energy to melt 500 kg o copper.

Fact 8) The Sun never sets on the ATLAS collaboration. Scientists working onthe experiment come rom every continent in the world, except Antarctica.

Fact 9) The CMS magnet system contains about 10 000 t o iron, which ismore iron than in the Eiel Tower.

Fact 10) The data recorded by each o the big experiments at the LHC will beenough to ll around 100 000 dual layer single-sided DVDs every year.

*) the total mass o protons is calculated at rest.

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Appendix 1

1.2 s 3.6 s

SPS Magnetic field

PSB Magnetic field

PS Magnetic field

SPS particle current

PS particle current

PSB particle current

Scheme o flling, magnetic feld and particle current inPSB, PS and SPS

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21.6 s SPS Magnetic field

Particle current in SPS

Particle current in one LHC ring

Appendix 2

Scheme o flling, magnetic feld and particle current inSPS and LHC

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The Publications Section wouldlike to thank those members othe AB, AT, PH Departments andSC who have helped to make this

Documents

Cern Lhc Guide