Collider (LHC) is the world's largest and most
powerful particle collider, the most complex experimental facility
ever built, and the largest single machine in the world. It was
built by the European Organization for Nuclear Research (CERN) between
1998 and 2008 in collaboration with over 10,000 scientists and
engineers from over 100 countries, as well as hundreds of universities
and laboratories. It lies in a tunnel 27 kilometres (17 mi) in
circumference, as deep as 175 metres (574 ft) beneath the
France–Switzerland border near Geneva. Its first research run took
place from March 2010 to early 2013 at an energy of 3.5 to
4 teraelectronvolts (TeV) per beam (7 to 8 TeV total), about
4 times the previous world record for a collider. Afterwards,
the accelerator was upgraded for two years. It was restarted in early
2015 for its second research run, reaching 6.5 TeV per beam (13 TeV
total, the present world record).
The aim of the LHC is to allow physicists to test the predictions of
different theories of particle physics, including measuring the
properties of the Higgs boson and searching for the large family of
new particles predicted by supersymmetric theories, as well as
other unsolved questions of physics.
The collider has four crossing points, around which are positioned
seven detectors, each designed for certain kinds of research. The LHC
primarily collides proton beams, but it can also use beams of heavy
ions. Proton–lead collisions were performed for short periods in
2013 and 2016, lead–lead collisions took place in 2010, 2011, 2013,
and 2015, and a short run of xenon–xenon collisions took place in
The LHC's computing grid is a world record holder.
collisions were produced at an unprecedented rate for the time of
first collisions, tens of petabytes per year, a major challenge at the
time, to be analysed by a grid-based computer network infrastructure
connecting 170 computing centres in 42 countries as of 2017
– by 2012 the
Worldwide LHC Computing Grid was also the world's
largest distributed computing grid, comprising over 170 computing
facilities in a worldwide network across 36 countries.
3.2 Computing and analysis facilities
4 Operational history
4.1.1 Operational challenges
4.1.3 Construction accidents and delays
4.1.4 Initial lower magnet currents
4.2 Inaugural tests (2008)
4.2.1 Quench incident
4.3 Run 1: first operational run (2009–2013)
4.4 Upgrade (2013–2015)
4.5 Run 2: second operational run (2015–2018)
5 Timeline of operations
6 Findings and discoveries
6.1 First run (data taken 2009–2013)
6.2 Second run (2015 onward)
7 Planned "high-luminosity" upgrade
8 Safety of particle collisions
9 Popular culture
10 See also
12 External links
The term hadron refers to composite particles composed of quarks held
together by the strong force (as atoms and molecules are held together
by the electromagnetic force). The best-known hadrons are the
baryons such as protons and neutrons; hadrons also include mesons such
as the pion and kaon, which were discovered during cosmic ray
experiments in the late 1940s and early 1950s.
A collider is a type of a particle accelerator with two directed beams
of particles. In particle physics, colliders are used as a research
tool: they accelerate particles to very high kinetic energies and let
them impact other particles. Analysis of the byproducts of these
collisions gives scientists good evidence of the structure of the
subatomic world and the laws of nature governing it. Many of these
byproducts are produced only by high-energy collisions, and they decay
after very short periods of time. Thus many of them are hard or nearly
impossible to study in other ways.
Physicists hope that the Large
Collider 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
interrelation between quantum mechanics and general relativity.
Data are also needed from high-energy particle experiments to suggest
which versions of current scientific models are more likely to be
correct – in particular to choose between the
Standard Model and
Higgsless model and to validate their predictions and allow further
theoretical development. Many theorists expect new physics beyond the
Standard Model to emerge at the TeV energy level, as the Standard
Model appears to be unsatisfactory. Issues explored by LHC collisions
is the mass of elementary particles being generated by the Higgs
mechanism via electroweak symmetry breaking? It was expected that
the collider experiments will either demonstrate or rule out the
existence of the elusive Higgs boson, thereby allowing physicists to
consider whether the
Standard Model or its Higgsless alternatives are
more likely to be correct. The ATLAS and CMS experiments
discovered the Higgs boson, which is strong evidence that the Standard
Model has the correct mechanism of giving mass to elementary
is supersymmetry, an extension of the
Standard Model and Poincaré
symmetry, realized in nature, implying that all known particles have
Are there extra dimensions, as predicted by various models based
on string theory, and can we detect them?
What is the nature of the dark matter that appears to account for 27%
of the mass-energy of the universe?
Other open questions that may be explored using high-energy particle
It is already known that electromagnetism and the weak nuclear force
are different manifestations of a single force called the electroweak
force. The LHC may clarify whether the electroweak force and the
strong nuclear force are similarly just different manifestations of
one universal unified force, as predicted by various Grand Unification
Why is the fourth fundamental force (gravity) so many orders of
magnitude weaker than the other three fundamental forces? See also
Are there additional sources of quark flavour mixing, beyond those
already present within the Standard Model?
Why are there apparent violations of the symmetry between matter and
antimatter? See also CP violation.
What are the nature and properties of quark–gluon plasma, thought to
have existed in the early universe and in certain compact and strange
astronomical objects today? This will be investigated by heavy ion
collisions, mainly in ALICE, but also in CMS, ATLAS and LHCb. First
observed in 2010, findings published in 2012 confirmed the phenomenon
of jet quenching in heavy-ion collisions.
Feynman diagram of one way the
Higgs boson may be produced at the
LHC. Here, two quarks each emit a W or Z boson, which combine to make
a neutral Higgs.
Map of the Large
Collider at CERN
The 2-in-1 structure of the LHC dipole magnets
The LHC is the world's largest and highest-energy particle
accelerator. The collider is contained in a circular tunnel,
with a circumference of 26.7 kilometres (16.6 mi), at a depth
ranging from 50 to 175 metres (164 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
Electron–Positron Collider. 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 beamlines (or beam
pipes) each containing a beam, which travel in opposite directions
around the ring. The beams intersect at four points around the ring,
which is where the particle collisions take place. Some 1,232 dipole
magnets keep the beams on their circular path (see image), while
an additional 392 quadrupole magnets are used to keep the beams
focused, with stronger quadrupole magnets close to the intersection
points in order to maximize the chances of interaction where the two
beams cross. Magnets of higher multipole orders are used to correct
smaller imperfections in the field geometry. In total, about 10,000
superconducting magnets are installed, with the dipole magnets having
a mass of over 27 tonnes. Approximately 96 tonnes of superfluid
helium-4 is needed to keep the magnets, made of copper-clad
niobium-titanium, at their operating temperature 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.
When running at the current energy record of 6.5 TeV per proton,
once or twice a day, as the protons are accelerated from 450 GeV
to 6.5 TeV, the field of the superconducting dipole magnets will
be increased from 0.54 to 7.7 teslas (T). The protons each have an
energy of 6.5 TeV, giving a total collision energy of
13 TeV. At this energy the protons have a
Lorentz factor of about
6,930 and move at about 0.999999990 c, or about 3.1 m/s
(11 km/h) slower than the speed of light (c). It takes less than
90 microseconds (μs) for a proton to travel 26.7 km around the main
ring. This results in 11,245 revolutions per second.
Rather than having continuous beams, the protons are bunched together,
into up to 2,808 bunches, with 115 billion protons in each bunch so
that interactions between the two beams take place at discrete
intervals, mainly 25 nanoseconds (ns) apart, providing a bunch
collision rate of 40 MHz. It was operated with fewer bunches in
the first years. The design luminosity of the LHC is 1034
cm−2s−1, which was first reached in June 2016. By 2017
twice this value was achieved.
Before being injected into the main accelerator, the particles are
prepared by a series of systems that successively increase their
energy. The first system is the linear particle accelerator 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
Proton Synchrotron (PS), where they are accelerated to 26 GeV.
Finally the Super
Proton Synchrotron (SPS) is used to increase their
energy further to 450 GeV before they are at last injected (over a
period of several minutes) into the main ring. Here the proton bunches
are accumulated, accelerated (over a period of 20 minutes) to their
peak energy, and finally circulated for 5 to 24 hours while collisions
occur at the four intersection points.
CMS detector for LHC
The LHC physics programme is mainly based on proton–proton
collisions. However, shorter running periods, typically one month per
year, with heavy-ion collisions are included in the programme. While
lighter ions are considered as well, the baseline scheme deals with
lead ions (see A Large Ion
Collider Experiment). The lead ions are
first accelerated by the linear accelerator LINAC 3, and the Low
Energy Ion Ring (LEIR) is used as an ion storage and cooler unit. The
ions are then further accelerated by the PS and SPS before being
injected into LHC ring, where they reached an energy of 2.3 TeV per
nucleon (or 522 TeV per ion), higher than the energies reached by
the Relativistic Heavy Ion Collider. The aim of the heavy-ion
programme is to investigate quark–gluon plasma, which existed in the
The LHC protons originate from the small red hydrogen tank.
See also: List of Large
Seven detectors have been constructed at the LHC, located underground
in large caverns excavated at the LHC's intersection points. Two of
ATLAS experiment and the
Compact Muon Solenoid
Compact Muon Solenoid (CMS), are
large general-purpose particle detectors. ALICE and
LHCb have more
specific roles and the last three, TOTEM,
MoEDAL and LHCf, are very
much smaller and are for very specialized research. The BBC's summary
of the main detectors is:
One of two general-purpose detectors. ATLAS studies the Higgs boson
and looks for signs of new physics, including the origins of mass and
The other general-purpose detector, like ATLAS, studies the Higgs
boson and look for clues of new physics.
ALICE is studying a "fluid" form of matter called quark–gluon plasma
that existed shortly after the Big Bang.
Equal amounts of matter and antimatter were created in the Big Bang.
LHCb investigates what happened to the "missing" antimatter.
Computing and analysis facilities
Main article: Worldwide LHC Computing Grid
Data produced by LHC, as well as LHC-related simulation, were
estimated at approximately 15 petabytes per year (max throughput while
running not stated) - a major challenge in its own right at the
The LHC Computing Grid was constructed as part of the LHC design,
to handle the massive amounts of data expected for its collisions. It
is an international collaborative project that consists of a
grid-based computer network infrastructure initially connecting 140
computing centres in 35 countries (over 170 in 36 countries as of
2012). It was designed by
CERN to handle the significant volume of
data produced by LHC experiments, incorporating both private
fibre optic cable links and existing high-speed portions of the public
Internet to enable 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 a computer
running Mac OS X,
Windows or Linux, to use their computer's idle time
to simulate how particles will travel in the beam pipes. With this
information, the scientists are able to determine how the magnets
should be calibrated to gain the most stable "orbit" of the beams in
the ring. In August 2011, a second application went live
(Test4Theory) which performs simulations against which to compare
actual test data, to determine confidence levels of the results.
By 2012 data from over 6 quadrillion (6 x 1015) LHC proton-proton
collisions had been analysed, LHC collision data was being
produced at approximately 25 petabytes per year, and the LHC Computing
Grid had become the world's largest computing grid (as of 2012),
comprising over 170 computing facilities in a worldwide network across
The LHC first went live on 10 September 2008, but initial testing
was delayed for 14 months from 19 September 2008 to 20 November 2009,
following a magnet quench incident that caused extensive damage to
over 50 superconducting magnets, their mountings, and the vacuum
During its first run (2010–2013) the LHC collided two opposing
particle beams of either protons at up to 4 teraelectronvolts (4
TeV or 0.64 microjoules), or lead nuclei (574 TeV per nucleus, or
2.76 TeV per nucleon). Its first run discoveries included the
long sought Higgs boson, several composite particles (hadrons) like
the χb (3P) bottomonium state, the first creation of a quark–gluon
plasma, and the first observations of the very rare decay of the Bs
meson into two muons (Bs0 → μ+μ−), which challenged the validity
of existing models of supersymmetry.
The size of the LHC constitutes an exceptional engineering challenge
with unique operational issues on account of the amount of energy
stored in the magnets and the beams. While operating, the
total energy stored in the magnets is 10 GJ (2,400 kilograms of
TNT) and the total energy carried by the two beams reaches 724 MJ
(173 kilograms of TNT).
Loss of only one ten-millionth part (10−7) of the beam is sufficient
to quench a superconducting magnet, while each of the two beam dumps
must absorb 362 MJ (87 kilograms of TNT). These energies are
carried by very little matter: under nominal operating conditions
(2,808 bunches per beam, 1.15×1011 protons per bunch), the beam pipes
contain 1.0×10−9 gram of hydrogen, which, in standard conditions
for temperature and pressure, would fill the volume of one grain of
See also: List of megaprojects
With a budget of €7.5 billion (approx. $9bn or £6.19bn as of
June 2010), the LHC is one of the most expensive scientific
instruments ever built. The total cost of the project is
expected to be of the order of 4.6bn Swiss francs (SFr) (approx.
$4.4bn, €3.1bn, or £2.8bn as of Jan 2010) for the accelerator
and 1.16bn (SFr) (approx. $1.1bn, €0.8bn, or £0.7bn as of
Jan 2010) for the
CERN contribution to the experiments.
The construction of LHC was approved in 1995 with a budget of SFr
2.6bn, with another SFr 210M toward the experiments. However, cost
overruns, estimated in a major review in 2001 at around SFr 480M for
the accelerator, and SFr 50M for the experiments, along with a
reduction in CERN's budget, pushed the completion date from 2005 to
April 2007. The superconducting magnets were responsible for SFr
180M of the cost increase. There were also further costs and delays
owing to engineering difficulties encountered while building the
underground cavern for the Compact
Muon Solenoid, and also due to
magnet supports which were insufficiently strongly designed and failed
their initial testing (2007) and damage from a magnet quench and
liquid helium escape (inaugural testing, 2008) (see: Construction
accidents and delays). Because electricity costs are lower during
the summer, the LHC normally does not operate over the winter
months, although exceptions over the 2009/10 and 2012/2013 winters
were made to make up for the 2008 start-up delays and to improve
precision of measurements of the new particle discovered in 2012,
Construction accidents and delays
On 25 October 2005, José Pereira Lages, a technician, was killed in
the LHC when a switchgear that was being transported fell on top of
On 27 March 2007 a cryogenic magnet support designed and provided by
KEK broke during an initial pressure test involving one
of the LHC's inner triplet (focusing quadrupole) magnet assemblies. No
one was injured.
Fermilab director Pier Oddone stated "In this case we
are dumbfounded that we missed some very simple balance of forces".
The fault had been present in the original design, and remained during
four engineering reviews over the following years. Analysis
revealed that its design, made as thin as possible for better
insulation, was not strong enough to withstand the forces generated
during pressure testing. Details are available in a statement from
Fermilab, with which
CERN is in agreement. Repairing the
broken magnet and reinforcing the eight identical assemblies used by
LHC delayed the start-up date, then planned for November 2007.
On 19 September 2008, during initial testing, a faulty electrical
connection led to a magnet quench (the sudden loss of a
superconducting magnet's superconducting ability owing to warming or
electric field effects). Six tonnes of supercooled liquid
helium—used to cool the magnets—escaped, with sufficient force to
break 10-ton magnets nearby from their mountings, and caused
considerable damage and contamination of the vacuum tube (see 2008
quench incident); repairs and safety checks caused a delay of around
Two vacuum leaks were found in July 2009, and the start of operations
was further postponed to mid-November 2009.
Initial lower magnet currents
Superconducting magnet §
In both of its runs (2010 to 2012 and 2015), the LHC was initially run
at energies below its planned operating energy, and ramped up to just
2 x 4 TeV energy on its first run and 2 x 6.5 TeV on its second run,
below the design energy of 2 x 7 TeV. This is because massive
superconducting magnets require considerable magnet training to handle
the high currents involved without losing their superconducting
ability, and the high currents are necessary to allow a high proton
energy. The "training" process involves repeatedly running the magnets
with lower currents to provoke any quenches or minute movements that
may result. It also takes time to cool down magnets to their operating
temperature of around 1.9 K (close to absolute zero). Over time the
magnet "beds in" and ceases to quench at these lesser currents and can
handle the full design current without quenching;
CERN media describe
the magnets as "shaking out" the unavoidable tiny manufacturing
imperfections in their crystals and positions that had initially
impaired their ability to handle their planned currents. The magnets,
over time and with training, gradually become able to handle their
full planned currents without quenching.
Inaugural tests (2008)
The first beam was circulated through the collider on the morning of
10 September 2008.
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. The LHC successfully completed its
major test: after a series of trial runs, two white dots flashed on a
computer screen showing the protons travelled the full length of the
collider. It took less than one hour to guide the stream of particles
around its inaugural circuit.
CERN next successfully sent a beam
of protons in an anticlockwise direction, taking slightly longer at
one and a half hours owing to a problem with the cryogenics, with the
full circuit being completed at 14:59.
Wikinews has related news:
CERN says repairs to LHC particle
accelerator to cost €16.6 million
On 19 September 2008, a magnet quench occurred in about 100 bending
magnets in sectors 3 and 4, where an electrical fault led to a loss of
approximately six tonnes of liquid helium (the magnets' cryogenic
coolant), which was vented into the tunnel. The escaping vapour
expanded with explosive force, damaging a total of 53 superconducting
magnets and their mountings, and contaminating the vacuum pipe, which
also lost vacuum conditions.
Shortly after the incident
CERN reported that the most likely cause of
the problem was a faulty electrical connection between two magnets,
and that – owing to the time needed to warm up the affected
sectors and then cool them back down to operating temperature –
it would take at least two months to fix.
CERN released an interim
technical report and preliminary analysis of the incident on 15
and 16 October 2008 respectively, and a more detailed report on 5
December 2008. The analysis of the incident by
CERN confirmed that
an electrical fault had indeed been the cause. The faulty electrical
connection had led (correctly) to a failsafe power abort of the
electrical systems powering the superconducting magnets, but had also
caused an electric arc (or discharge) which damaged the integrity of
the supercooled helium's enclosure and vacuum insulation, causing the
coolant's temperature and pressure to rapidly rise beyond the ability
of the safety systems to contain it, and leading to a temperature
rise of about 100 degrees
Celsius in some of the affected magnets.
Energy stored in the superconducting magnets and electrical noise
induced in other quench detectors also played a role in the rapid
heating. Around two tonnes of liquid helium escaped explosively before
detectors triggered an emergency stop, and a further four tonnes
leaked at lower pressure in the aftermath. A total of 53 magnets
were damaged in the incident and were repaired or replaced during the
winter shutdown. This accident was thoroughly discussed in a
22 February 2010
Superconductor Science and Technology article by
CERN physicist Lucio Rossi.
In the original timeline of the LHC commissioning, the first "modest"
high-energy collisions at a centre-of-mass energy of 900 GeV were
expected to take place before the end of September 2008, and the LHC
was expected to be operating at 10 TeV by the end of 2008.
However, owing to the delay caused by the above-mentioned incident,
the collider was not operational until November 2009. Despite the
delay, LHC was officially inaugurated on 21 October 2008, in the
presence of political leaders, science ministers from CERN's 20 Member
CERN officials, and members of the worldwide scientific
Most of 2009 was spent on repairs and reviews from the damage caused
by the quench incident, along with two further vacuum leaks identified
in July 2009 which pushed the start of operations to November of that
Run 1: first operational run (2009–2013)
Seminar on the physics of LHC by
John Iliopoulos (2009).
On 20 November 2009, low-energy beams circulated in the tunnel for the
first time since the incident, and shortly after, on 30 November, the
LHC achieved 1.18 TeV per beam to become the world's
highest-energy particle accelerator, beating the Tevatron's previous
record of 0.98 TeV per beam held for eight years.
The early part of 2010 saw the continued ramp-up of beam in energies
and early physics experiments towards 3.5 TeV per beam and on 30
March 2010, LHC set a new record for high-energy collisions by
colliding proton beams at a combined energy level of 7 TeV. The
attempt was the third that day, after two unsuccessful attempts in
which the protons had to be "dumped" from the collider and new beams
had to be injected. This also marked the start of the main
The first proton run ended on 4 November 2010. A run with lead ions
started on 8 November 2010, and ended on 6 December 2010, allowing
ALICE experiment to study matter under extreme conditions similar
to those shortly after the Big Bang.
CERN originally planned that the LHC would run through to the end of
2012, with a short break at the end of 2011 to allow for an increase
in beam energy from 3.5 to 4 TeV per beam. At the end of 2012
the LHC was planned to get shut down until around 2015 to allow
upgrade to a planned beam energy of 7 TeV per beam. In late
2012, in light of the July 2012 discovery of the Higgs boson, the
shutdown was postponed for some weeks into early 2013, to allow
additional data to be obtained before shutdown.
The LHC was shut down on 13 February 2013 for its 2-year upgrade,
which was to touch on many aspects of the LHC: enabling collisions at
14 TeV, enhancing its detectors and pre-accelerators (the Proton
Synchrotron and Super
Proton Synchrotron), as well as replacing its
ventilation system and 100 km of cabling impaired by high-energy
collisions from its first run. The upgraded collider began its
long start-up and testing process in June 2014, with the Proton
Synchrotron Booster starting on 2 June 2014, the final interconnection
between magnets completing and the
Proton Synchrotron circulating
particles on 18 June 2014, and the first section of the main LHC
supermagnet system reaching operating temperature of 1.9 K
(−271.25 °C), a few days later. Due to the slow progress
with "training" the superconducting magnets, it was decided to start
the second run with a lower energy of 6.5 TeV per beam, corresponding
to a current of 11,000 amperes. The first of the main LHC magnets were
reported to have been successfully trained by 9 December 2014, while
training the other magnet sectors was finished in March 2015.
Run 2: second operational run (2015–2018)
On 5 April 2015, the LHC restarted after a two-year break, during
which the electrical connectors between the bending magnets were
upgraded to safely handle the current required for 7 TeV per beam (14
TeV). However, the bending magnets were only trained to handle
up to 6.5 TeV per beam (13 TeV total), which became the operating
energy for 2015 to 2017. The energy was first reached on 10 April
2015. The upgrades culminated in colliding protons together with
a combined energy of 13 TeV. On 3 June 2015 the LHC started
delivering physics data after almost two years offline. In the
following months it was used for proton-proton collisions, while in
November the machine switched to collisions of lead ions and in
December the usual winter shutdown started.
In 2016, the machine operators focused on increasing the luminosity
for proton-proton collisions. The design value was first reached 29
June, and further improvements increased the collision rate to 40%
above the design value. The total number of collisions in 2016
exceeded the number from Run 1 - at a higher energy per collision. The
proton-proton run was followed by four weeks of proton-lead
In 2017 the luminosity could be increased further and reached twice
the design value. The total number of collisions was higher than in
2016 as well.
Timeline of operations
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
First "modest" high-energy collisions planned but postponed due to
16 Oct 2008
CERN released a preliminary analysis of the accident.
21 Oct 2008
5 Dec 2008
CERN released detailed analysis.
20 Nov 2009
Low-energy beams circulated in the tunnel for the first time since the
23 Nov 2009
First particle collisions in all four detectors at 450 GeV.
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.
15 Dec 2009
First scientific results, covering 284 collisions in the ALICE
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 programme.
8 Nov 2010
Start of the first run with lead ions.
6 Dec 2010
End of the run with lead ions. Shutdown until early 2011.
13 Mar 2011
Beginning of the 2011 run with proton beams.
21 Apr 2011
LHC becomes the world's highest-luminosity hadron accelerator
achieving a peak luminosity of 4.67·1032 cm−2s−1, beating
the Tevatron's previous record of 4·1032 cm−2s−1 held for
24 May 2011
ALICE reports that a
Quark–gluon plasma has been achieved with
earlier lead collisions.
17 Jun 2011
The high-luminosity experiments ATLAS and CMS reach 1 fb−1 of
14 Oct 2011
LHCb reaches 1 fb−1 of collected data.
23 Oct 2011
The high-luminosity experiments ATLAS and CMS reach 5 fb−1 of
Second run with lead ions.
22 Dec 2011
First new composite particle discovery, the χb (3P) bottomonium
meson, observed with proton-proton collisions in 2011.
5 Apr 2012
First collisions with stable beams in 2012 after the winter shutdown.
The energy is increased to 4 TeV per beam (8 TeV in collisions).
4 Jul 2012
First new elementary particle discovery, a new boson observed that is
"consistent with" the theorized Higgs boson. (This has now been
confirmed as the
Higgs boson itself.)
8 Nov 2012
First observation of the very rare decay of the Bs meson into two
muons (Bs0 → μ+μ−), a major test of supersymmetry theories,
shows results at 3.5 sigma that match the
Standard Model rather than
many of its super-symmetrical variants.
20 Jan 2013
Start of the first run colliding protons with lead ions.
11 Feb 2013
End of the first run colliding protons with lead ions.
14 Feb 2013
Beginning of the first long shutdown to prepare the collider for a
higher energy and luminosity.
7 Mar 2015
Injection tests for Run 2 send protons towards
LHCb & ALICE
5 Apr 2015
Both beams circulated in the collider. Four days later, a new
record energy of 6.5 TeV per proton was achieved.
20 May 2015
Protons collided in the LHC at the record-breaking collision energy of
3 Jun 2015
Start of delivering the physics data after almost two years offline
4 Nov 2015
End of proton collisions in 2015, start of preparations for ion
25 Nov 2015
First ion collisions at a record-breaking energy of more than 1 PeV
13 Dec 2015
End of ion collisions in 2015
23 Apr 2016
Data-taking in 2016 begins
29 June 2016
The LHC achieves a luminosity of 1.0 · 1034 cm−2s−1, its
design value. Further improvements over the year increased the
luminosity to 40% above the design value.
26 Oct 2016
End of 2016 proton-proton collisions
10 Nov 2016
Beginning of 2016 proton-lead collisions
3 Dec 2016
End of 2016 proton-lead collisions
24 May 2017
Start of 2017 proton-proton collisions. During 2017, the luminosity
increased to twice its design value.
10 Nov 2017
End of regular 2017 proton-proton collision mode.
Findings and discoveries
An initial focus of research was to investigate the possible existence
of the Higgs boson, a key part of the
Standard Model of physics which
is predicted by theory but had not yet been observed before due to its
high mass and elusive nature.
CERN scientists estimated that, if the
Standard Model were correct, the LHC would produce several Higgs
bosons every minute, allowing physicists to finally confirm or
disprove the Higgs boson's existence. In addition, the LHC allowed the
search for supersymmetric particles and other hypothetical particles
as possible unknown areas of physics. Some extensions of the
Standard Model predict additional particles, such as the heavy W' and
Z' gauge bosons, which are also estimated to be within reach of the
LHC to discover.
First run (data taken 2009–2013)
The first physics results from the LHC, involving 284 collisions which
took place in the ALICE detector, were reported on 15 December
2009. The results of the first proton–proton collisions at
energies higher than Fermilab's
collisions were published by the CMS collaboration in early February
2010, yielding greater-than-predicted charged-hadron production.
After the first year of data collection, the LHC experimental
collaborations started to release their preliminary results concerning
searches for new physics beyond the
Standard Model in proton-proton
collisions. No evidence of new particles was
detected in the 2010 data. As a result, bounds were set on the allowed
parameter space of various extensions of the Standard Model, such as
models with large extra dimensions, constrained versions of the
Minimal Supersymmetric Standard Model, and others.
On 24 May 2011, it was reported that quark–gluon plasma (the densest
matter thought to exist besides black holes) had been created in the
Between July and August 2011, results of searches for the Higgs boson
and for exotic particles, based on the data collected during the first
half of the 2011 run, were presented in conferences in Grenoble
and Mumbai. In the latter conference it was reported that,
despite hints of a Higgs signal in earlier data, ATLAS and CMS exclude
with 95% confidence level (using the CLs method) the existence of a
Higgs boson with the properties predicted by the
Standard Model over
most of the mass region between 145 and 466 GeV. The searches for
new particles did not yield signals either, allowing to further
constrain the parameter space of various extensions of the Standard
Model, including its supersymmetric extensions.
On 13 December 2011,
CERN reported that the
Standard Model Higgs
boson, if it exists, is most likely to have a mass constrained to the
range 115–130 GeV. Both the CMS and ATLAS detectors have also shown
intensity peaks in the 124–125 GeV range, consistent with either
background noise or the observation of the Higgs boson.
On 22 December 2011, it was reported that a new composite particle had
been observed, the χb (3P) bottomonium state.
On 4 July 2012, both the CMS and ATLAS teams announced the discovery
of a boson in the mass region around 125–126 GeV, with a statistical
significance at the level of 5 sigma each. This meets the formal level
required to announce a new particle. The observed properties were
consistent with the Higgs boson, but scientists were cautious as to
whether it is formally identified as actually being the Higgs boson,
pending further analysis.
On 8 November 2012, the
LHCb team reported on an experiment seen as a
"golden" test of supersymmetry theories in physics, by measuring
the very rare decay of the Bs meson into two muons (Bs0 → μ+μ−).
The results, which match those predicted by the non-supersymmetrical
Standard Model rather than the predictions of many branches of
supersymmetry, show the decays are less common than some forms of
supersymmetry predict, though could still match the predictions of
other versions of supersymmetry theory. The results as initially
drafted are stated to be short of proof but at a relatively high 3.5
sigma level of significance. The result was later confirmed by
the CMS collaboration.
In August 2013 the
LHCb team revealed an anomaly in the angular
B meson decay products which could not be predicted by
the Standard Model; this anomaly had a statistical certainty of 4.5
sigma, just short of the 5 sigma needed to be officially recognized as
a discovery. It is unknown what the cause of this anomaly would be,
Z' boson has been suggested as a possible candidate.
On 19 November 2014, the
LHCb experiment announced the discovery of
two new heavy subatomic particles, Ξ′−
b and Ξ∗−
b. Both of them are baryons that are composed of one bottom, one down,
and one strange quark. They are excited states of the bottom Xi
LHCb collaboration has observed multiple exotic hadrons, possibly
pentaquarks or tetraquarks, in the Run 1 data. On 4 April 2014, the
collaboration confirmed the existence of the tetraquark candidate
Z(4430) with a significance of over 13.9 sigma. On 13 July
2015, results consistent with pentaquark states in the decay of bottom
Lambda baryons (Λ0
b) were reported. On 28 June 2016, the collaboration
announced four tetraquark-like particles decaying into a J/ψ and a φ
meson, only one of which was well established before (X(4274), X(4500)
and X(4700) and X(4140)).
In December 2016, ATLAS presented a measurement of the W boson mass,
researching the precision of analyses done at the Tevatron.
Second run (2015 onward)
At the conference EPS-HEP 2015 in July, the collaborations presented
first cross-section measurements of several particles at the higher
On 15 December 2015, the ATLAS and CMS experiments both reported a
number of preliminary results for Higgs physics, supersymmetry (SUSY)
searches and exotics searches using 13 TeV proton collision data. Both
experiments saw a moderate excess around 750 GeV in the two-photon
invariant mass spectrum, but the experiments did not
confirm the existence of the hypothetical particle in an August 2016
In July 2017, many analysis based on the large dataset collected in
2016 were shown. The properties of the
Higgs boson were studied in
more detail and the precision of many other results was improved.
Planned "high-luminosity" upgrade
Main article: High Luminosity Large
After some years of running, any particle physics experiment typically
begins to suffer from diminishing returns: as the key results
reachable by the device begin to be completed, later years of
operation discover proportionately less than earlier years. A common
response is to upgrade the devices involved, typically in collision
energy, luminosity, or improved detectors. In addition to a possible
increase to 14 TeV collision energy in 2018, a luminosity upgrade
of the LHC, called the High Luminosity LHC, is planned, to be
made after 2022.
Safety of particle collisions
Main article: Safety of high-energy particle collision experiments
The experiments at the Large
Collider sparked fears that the
particle collisions might produce doomsday phenomena, involving the
production of stable microscopic black holes or the creation of
hypothetical particles called strangelets. Two CERN-commissioned
safety reviews examined these concerns and concluded that the
experiments at the LHC present no danger and that there is no reason
for concern, a conclusion expressly endorsed by the
American Physical Society.
The reports also noted that the physical conditions and collision
events that exist in the LHC and similar experiments occur naturally
and routinely in the universe without hazardous consequences,
including ultra-high-energy cosmic rays observed to impact Earth with
energies far higher than those in any man-made collider.
Collider gained a considerable amount of attention
from outside the scientific community and its progress is followed by
most popular science media. The LHC has also inspired works of fiction
including novels, TV series, video games and films.
CERN employee Katherine McAlpine's "Large
Hadron Rap" surpassed
YouTube views. The band Les Horribles
Cernettes was founded by women from CERN. The name was chosen so to
have the same initials as the LHC.
National Geographic Channel's World's Toughest Fixes, Season 2 (2010),
Episode 6 "
Atom Smasher" features the replacement of the last
superconducting magnet section in the repair of the collider after the
2008 quench incident. The episode includes actual footage from the
repair facility to the inside of the collider, and explanations of the
function, engineering, and purpose of the LHC.
Collider was the focus of the 2012 student film
Decay, with the movie being filmed on location in CERN's maintenance
The feature documentary
Particle Fever follows the experimental
CERN who run the experiments, as well as the theoretical
physicists who attempt to provide a conceptual framework for the LHC's
results. It won the Sheffield International Doc/Fest in 2013.
The novel Angels & Demons, by Dan Brown, involves antimatter
created at the LHC to be used in a weapon against the Vatican. In
CERN published a "Fact or Fiction?" page discussing the
accuracy of the book's portrayal of the LHC, CERN, and particle
physics in general. The movie version of the book has footage
filmed on-site at one of the experiments at the LHC; the director, Ron
Howard, met with
CERN experts in an effort to make the science in the
story more accurate.
In the visual novel/manga/anime-series "Steins;Gate", the primary
antagonist controls a global research organization called SERN, the
name of which is a deliberate misspelling of CERN. In the series SERN
designs a particle accelerator and uses the miniature black holes
created from experiments to master time travel and take over the
The novel FlashForward, by Robert J. Sawyer, involves the search for
Higgs boson at the LHC.
CERN published a "Science and Fiction"
page interviewing Sawyer and physicists about the book and the TV
series based on it.
Compact Linear Collider
International Linear Collider
List of accelerators in particle physics
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Wikimedia Commons has media related to Large
Overview of the LHC at CERN's public webpage
CERN Courier magazine
Portal Web portal
Lyndon Evans and Philip Bryant (eds) (2008). "LHC Machine". Journal of
Instrumentation. 3 (8): S08001. Bibcode:2008JInst...3S8001E.
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authors list (link) Full documentation for design and construction of
the LHC and its six detectors (2008).
CERN, how LHC works on YouTube
"Petabytes at the LHC". Sixty Symbols.
Brady Haran for the University
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Eight Things To Know As The Large
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