Large Hadron Collider
Large Hadron Collider
Large Hadron Collider
4614N 0603E
LHC experiments
ATLAS
CMS
LHCb
LHC-beauty
ALICE
TOTEM
LHCf
LHC-forward
MoEDAL
LHC preaccelerators
p and Pb
(not marked)
PS
Proton Synchrotron
SPS
Hadron colliders
Intersecting Storage Rings
CERN, 19711984
CERN, 19811984
ISABELLE
Tevatron
Fermilab, 1987present
BNL, 2000present
Cancelled in 1993
CERN, 2009present
Theoretical
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle
accelerator. It is expected to address some of the most fundamental
questions of physics, advancing the understanding of the deepest laws of nature.
The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as deep as 175 metres
(574 ft) beneath the Franco-Swiss border near Geneva, Switzerland. This synchrotron is
designed to collide opposing particle beams of either protons at an energy of
7 teraelectronvolts (7 TeV or 1.12microjoules) per particle, or lead nuclei at an energy of
574 TeV (92.0 J) per nucleus.[1][2] The term hadron refers to particles composed
of quarks.
The Large Hadron Collider was built by the European Organization for Nuclear
Research (CERN) with the intention of testing various predictions of high-energy
physics, including testing for the existence of the hypothesized Higgs boson[3] and of the
On 30 March 2010, the first planned collisions took place between two 3.5 TeV
beams, a new world record for the highest-energy man-made particle collisions. [12] The
LHC will continue to operate at half energy for some years; it will not be running at full
energy (7 TeV per beam) until 2014.[13]
Contents
[hide]
1 Purpose
2 Design
2.1 Detectors
3 Operational history
4 Timeline
5 Findings
6 Proposed upgrade
7 Cost
8 Computing resources
9 Safety of particle collisions
10 Operational challenges
11 Construction accidents and delays
12 Popular culture
13 See also
14 References
15 External links
[edit]Purpose
A simulated event in the CMS detector, featuring the appearance of the Higgs boson
Physicists hope that the LHC will help answer some of the fundamental open
questions in physics, concerning the basic laws governing the interactions and forces
among the elementary objects, the deep structure of space and time, and in particular
the intersection of quantum mechanics and general relativity, where current theories and
knowledge are unclear or break down altogether. Data is also needed from high energy
particle experiments to indicate which versions of scientific models are more likely to be
correct - in particular to choose between the Standard Model and Higgsless models and
to validate their predictions and allow further theoretical development. Many theorists
expect new physics beyond the Standard Model to emerge at the TeV-scale, based on
unsatisfactory properties of the Standard Model. Issues possibly to be explored by LHC
collisions include:[14]
What is the nature of the dark matter that appears to account for 23% of the
mass of the universe?
Other open questions which may be explored using high energy particle collisions:
Are electromagnetism, the strong nuclear force and the weak nuclear
force just different manifestations of a single unified force, as predicted by
variousGrand Unification Theories?
Are there additional sources of quark flavour mixing, beyond those already
predicted within the Standard Model?
What are the nature and properties of quark-gluon plasma, believed to have
existed in the early universe and in certain compact and strangeastronomical
objects today? This will be investigated by heavy ion collisions in ALICE.
[edit]Design
A Feynman diagram of one way theHiggs boson may be produced at the LHC. Here, two quarks each emit
a W or Z boson, which combine to make a neutral Higgs.
The LHC is the world's largest and highest-energy particle accelerator.[1][24] The
collider is contained in a circular tunnel, with a circumference of 27 kilometres
(17 mi), at a depth ranging from 50 to 175 metres (160 to 574 ft) underground.
The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between 1983 and
1988, was formerly used to house the Large ElectronPositron Collider.[25] It
crosses the border between Switzerland and France at four points, with most of it
in France. Surface buildings hold ancillary equipment such as compressors,
ventilation equipment, control electronics and refrigeration plants.
The collider tunnel contains two adjacent parallel beam pipes that intersect at
four points, each containing a proton beam, which travel in opposite directions
around the ring. Some 1,232 dipole magnets keep the beams on their circular
path, while an additional 392 quadrupole magnets are used to keep the beams
focused, in order to maximize the chances of interaction between the particles in
the four intersection points, where the two beams will cross. In total,
over 1,600 superconducting magnets are installed, with most weighing over 27
tonnes. Approximately 96 tonnes of liquid helium is needed to keep the magnets,
made of copper-clad niobium-titanium, at their operating temperature of 1.9
K (271.25 C), making the LHC the largest cryogenic facility in the world at
liquid helium temperature.
Superconducting quadrupole electromagnets are used to direct the beams to four intersection points, where
interactions between accelerated protons will take place.
Once or twice a day, as the protons are accelerated from 450 GeV to 7 TeV, the
field of the superconducting dipole magnets will be increased from 0.54
to 8.3 teslas (T). The protons will each have an energy of 7 TeV, giving a total
collision energy of 14 TeV. At this energy the protons have a Lorentz factor of
about 7,500 and move at about0.999999991 c, or about 3 metres per second
slower than the speed of light (c).[26] It will take less than90 microseconds (s) for
a proton to travel once around the main ring a speed of about 11,000
revolutions per second. Rather than continuous beams, the protons will be
bunched together, into 2,808 bunches, so that interactions between the two
beams will take place at discrete intervals never shorter
than25 nanoseconds (ns) apart. However it will be operated with fewer bunches
when it is first commissioned, giving it a bunch crossing interval of 75 ns.[27] The
design luminosity of the LHC is 1034 cm2s1, providing a bunch collision rate of
40 MHz.[28]
Prior to being injected into the main accelerator, the particles are prepared by a
series of systems that successively increase their energy. The first system is
the linear particle accelerator LINAC 2 generating 50-MeV protons, which feeds
the Proton Synchrotron Booster (PSB). There the protons are accelerated to 1.4
GeV and injected into the Proton Synchrotron (PS), where they are accelerated
to 26 GeV. Finally the Super Proton Synchrotron (SPS) is used to further
increase their energy to 450 GeV before they are at last injected (over a period of
20 minutes) into the main ring. Here the proton bunches are accumulated,
accelerated (over a period of 20 minutes) to their peak 7-TeV energy, and finally
circulated for 10 to 24 hours while collisions occur at the four intersection points.
[29]
Description
ATLAS
one of two general purpose detectors. ATLAS will be used to look for signs of new physics,
including the origins of mass and extra dimensions.
CMS
the other general purpose detector will, like ATLAS, hunt for the Higgs boson and look for clues to
the nature of dark matter.
ALICE
is studying a "fluid" form of matter called quarkgluon plasma that existed shortly after the Big
Bang.
LHCb
equal amounts of matter and antimatter were created in the Big Bang. LHCb will try to investigate
what happened to the "missing" antimatter.
[edit]Operational
history
The first beam was circulated through the collider on the morning of 10
September 2008.[31] CERN successfully fired the protons around the tunnel in
stages, three kilometres at a time. The particles were fired in a clockwise
direction into the accelerator and successfully steered around it at 10:28 local
time.[32] The LHC successfully completed its first major test: after a series of trial
runs, two white dots flashed on a computer screen showing the protons travelled
the full length of the collider. It took less than one hour to guide the stream of
particles around its inaugural circuit.[33] CERN next successfully sent a beam of
protons in a counterclockwise direction, taking slightly longer at one and a half
hours due to a problem with the cryogenics, with the full circuit being completed
at 14:59.
On 19 September 2008, a quench occurred in about 100 bending magnets in
sectors 3 and 4, causing a loss of approximately six tonnes of liquid helium,
which was vented into the tunnel, and a temperature rise of about 100 kelvin in
some of the affected magnets. Vacuum conditions in the beam pipe were also
lost.[34] Shortly after the incident CERN reported that the most likely cause of the
problem was a faulty electrical connection between two magnets, and that due
to the time needed to warm up the affected sectors and then cool them back
down to operating temperature it would take at least two months to fix it.
[35]
October 2008,[36] and a more detailed one on 5 December 2008.[37] Both analyses
confirmed that the incident was indeed initiated by a faulty electrical connection.
A total of 53 magnets were damaged in the incident and were repaired or
replaced during the winter shutdown. [38]
In the original timeline of the LHC commissioning, the first "modest" high-energy
collisions at a center-of-mass energy of 900 GeV were expected to take place
before the end of September 2008, and the LHC was expected to be operating at
10 TeV by the time of the official inauguration on 21 October 2008. [39] However,
due to the delay caused by the above-mentioned incident, the collider was not
operational until November 2009.[40] Despite the delay, LHC was officially
inaugurated on 21 October 2008, in the presence of political leaders, science
ministers from CERN's 20 Member States, CERN officials, and members of the
worldwide scientific community.[41]
Most of 2009 was spent on repairs and reviews from the damage caused by the
quench incident. On November 20, low-energy beams circulated in the tunnel for
the first time since the incident. The early part of 2010 saw the continued ramp-
This allowed the ALICE experiment to study matter under extreme conditions
Date
Event
10 Sep 2008
CERN successfully fired the first protons around the entire tunnel circuit in stages.
19 Sep 2008
Magnetic quench occurred in about 100 bending magnets in sectors 3 and 4, causing a loss of
approximately 6 tonnes of liquid helium.
30 Sep 2008
16 Oct 2008
21 Oct 2008
Official inauguration.
5 Dec 2008
20 Nov 2009 Low-energy beams circulated in the tunnel for the first time since the accident.[45]
23 Nov 2009 First particle collisions in all four detectors at 450 GeV.[9]
30 Nov 2009
LHC becomes the world's highest-energy particle accelerator achieving 1.18 TeV per beam,
beating the Tevatron's previous record of 0.98 TeV per beam held for eight years.[46]
28 Feb 2010
The LHC continues operations ramping energies to run at 3.5 TeV for 18 months to two years,
after which it will be shut down to prepare for the 14 TeV collisions (7 TeV per beam).[47]
30 Mar 2010
The two beams collided at 7 TeV (3.5 TeV per beam) in the LHC at 13:06 CEST, marking the
start of the LHC research program.
8 Nov 2010
6 Dec 2010
End of the run with lead ions. Shutdown until early 2011.
13 Mar 2011
21 Apr 2011
LHC becomes the world's highest-luminosity hadron accelerator achieving a peak luminosity of
4.671032 cm2s1, beating the Tevatron's previous record of 41032 cm2s1 held for one year.[49]
17 Jun 2011
The high luminosity experiments ATLAS and CMS reach 1 fb-1 of collected data.[50]
[edit]Findings
CERN scientists estimate that, if the Standard Model is correct, a single Higgs
boson may be produced every few hours. At this rate, it may take about two to
three years to collect enough data to discover the Higgs boson unambiguously.
Similarly, it may take one year or more before sufficient results
concerning supersymmetric particles have been gathered to draw meaningful
conclusions.[1]On the other hand, some extensions of the Standard Model predict
additional particles, such as the heavy W' and Z' gauge bosons, whose existence
might already be probed after a few months of data taking. [51]
The first physics results from the LHC, involving 284 collisions which took place
in the ALICE detector, were reported on 15 December 2009.[52] The results of the
first protonproton collisions at energies higher than Fermilab's Tevatron proton
antiproton collisions were published by the CMS collaboration in early February
2010, yielding greater-than-predicted charged-hadron production.[53]
After the first year of data taking, the LHC experimental collaborations started to
release their preliminary results concerning searches for new physics beyond the
Standard Model in proton-proton collisions. [54][55][56][57] So far, no evidence of new
particles has been detected. As a result, bounds can be set on the allowed
parameter space of various extensions of the Standard Model, such as models
upgrade
With a budget of 7.5 billion euros (approx. $9bn or 6.19bn as of Jun 2010), the
LHC is one of the most expensive scientific instruments [64] ever built.[65] The total
cost of the project is expected to be of the order of 4.6bn Swiss francs (approx.
$4.4bn, 3.1bn, or 2.8bn as of Jan 2010) for the accelerator and SFr 1.16bn
(approx. $1.1bn, 0.8bn, or 0.7bn as of Jan 2010) for the CERN contribution to
the experiments.[66]
The construction of LHC was approved in 1995 with a budget of SFr 2.6bn, with
another SFr 210M towards the experiments. However, cost overruns, estimated
in a major review in 2001 at around SFr 480M for the accelerator, and SFr 50M
for the experiments, along with a reduction in CERN's budget, pushed the
completion date from 2005 to April 2007.[67] The superconducting magnets were
responsible for SFr 180M of the cost increase. There were also further costs and
delays due to engineering difficulties encountered while building the underground
cavern for the Compact Muon Solenoid,[68] and also due to faulty parts provided
by Fermilab.[69] Due to lower electricity costs during the summer, it is expected
that the LHC will normally not operate over the winter months, [70]although an
exception was made to make up for the 2008 start-up delays over the 2009/10
winter.
[edit]Computing
resources
The LHC Computing Grid[72] is being constructed to handle the massive amounts
of data produced. It incorporates both private fiber optic cable links and existing
high-speed portions of the publicInternet, enabling data transfer from CERN to
academic institutions around the world.
The Open Science Grid is used as the primary infrastructure in the United States,
and also as part of an interoperable federation with the LHC Computing Grid.
The distributed computing project LHC@home was started to support the
construction and calibration of the LHC. The project uses the BOINC platform,
enabling anybody with an Internet connection and either Windows, Mac OS
X or Linux to use their computer's idle time 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.[73]
[edit]Safety
of particle collisions
challenges
magnets and the beams.[29][79] While operating, the total energy stored in the
magnets is 10 GJ (equivalent to 2.4 tons of TNT) and the total energy carried by
the two beams reaches 724 MJ (173 kilograms of TNT).[80]
Loss of only one ten-millionth part (107) of the beam is sufficient
to quench a superconducting magnet, while the beam dump must absorb 362 MJ
(87 kilograms of TNT) for each of the two beams. These energies are carried by
very little matter: under nominal operating conditions (2,808 bunches per beam,
1.151011 protons per bunch), the beam pipes contain 1.010 9 gram of
hydrogen, which, in standard conditions for temperature and pressure, would fill
the volume of one grain of fine sand.
[edit]Construction
On 25 October 2005, Jos Pereira Lages, a technician, was killed in the LHC
when a switchgear that was being transported fell on him.[81]
surrounding vacuum layer with sufficient force to break 10-ton magnets from
their mountings. The explosion also contaminated the proton tubes with soot.
[37][86]
Two vacuum leaks were identified in July 2009, and the start of operations
was further postponed to mid-November 2009.[88]
[edit]Popular
culture