CERN and the European Committee for Future Accelerators (ECFA) hold a workshop in Lausanne, Switzerland and at CERN from the 21-27 March 1984. The event, Large Hadron Collider in the LEP Tunnel, marks the first official recognition of the concept of the LHC. Attendees consider topics such as what types of particles to collide and the challenges inherent to high-energy collisions. The image above shows one proposal from the workshop – adding the LHC in with the existing LEP machine – that was later scrapped.   Read the workshop proceedings

With US President Ronald Reagan’s support, American physicists begin in-depth preparations to build the largest particle collider ever. The Superconducting Super Collider (SSC) – a circular accelerator with an 87-kilometre circumference – is designed to smash particles together at 40 TeV centre-of-mass energy. This would make the accelerator far more powerful than CERN's planned Large Hadron Collider (LHC). Construction begins in 1991 near Waxahachie, Texas. To some, the existence of the SSC project puts the need to build the LHC into doubt. Director-General Carlo Rubbia has to push to keep the LHC project alive.

The Toroidal LHC Apparatus collaboration propose to build a multipurpose detector at the LHC. The letter of intent they submit to the LHC Experiments Committee marks the first official use of the name ATLAS. Two collaborations called ASCOT and EAGLE combine to form ATLAS. Read the ATLAS letter of intent The Compact Muon Solenoid (CMS) collaboration proposes to build a multipurpose detector at the LHC. The letter of intent they submit to the LHC Experiments Committee marks the first official use of the name CMS. Read the CMS letter of intent

The collaboration for A Large Ion Collider Experiment (ALICE) propose to build a detector at the LHC to study heavy-ion collisions. The letter of intent marks the first official use of the name ALICE. Read the ALICE letter of intent

Due to concerns linked to rising costs, the US government votes to cancel the Superconducting Super Collider project. The LHC becomes the sole candidate for a new high-energy hadron collider.

The first prototype bending-magnet for the LHC reaches a field of 8.73 Tesla, which is higher than the 8.4 Tesla field at which the LHC will operate in 2012. Superconducting magnets must be "trained" so that they can maintain the superconducting state necessary to achieve such high fields. Any abnormal termination of the superconducting state, which switches the magnet back to its normal, resistive state, is called a "quench." LHC Director Lyn Evans receives a hand-written note as he sits in a Finance Committee meeting. It reads: Message de J.P Goubier et R.Perin à L Evans on a attaint 8,73 tesla100 quench They mean "sans quench" - a pun on the French word "cent" or "one hundred", which is pronounced the same as the word for "without".

The CERN council approves the construction of the Large Hadron Collider. To achieve the project without enlarging CERN’s budget, they decide to build the accelerator in two stages.

The CERN Council admits Japan as an observer state. Japan announces a financial contribution to the LHC. The Japanese Minister for Education, Sciences and Culture offers a Daruma doll to CERN’s Director-General. According to Japanese tradition, an eye is painted on the doll to mark the beginning of the LHC project and the second eye must be drawn at the time of its completion. Japan makes two other major financial contributions to the LHC project in 1996 and 1998.

The Large Hadron Collider (LHC) project is approved by the CERN council in December 1994. The LHC study group publish the LHC Conceptual Design Report, which details the architecture and operation of the LHC, in October 1995.

Four years after the first technical proposals, the experiments CMS and ATLAS are officially approved. Both are general-purpose experiments designed to explore the fundamental nature of matter and the basic forces that shape our universe, including the Higgs boson.

The CERN research board officially approves the ALICE experiment. Re-using the L3 magnet experiment from the LEP, ALICE is designed to study quark-gluon plasma, a state of matter that would have existed in the first moments of the universe.

The Total Cross Section, Elastic Scattering Diffraction Dissociation collaboration proposes to build a detector to measure the basic properties of proton-proton collisions at high energy. The letter of intent marks the first official use of the name TOTEM. Read the TOTEM letter of intent

At the December session of the CERN council, representatives of the United States sign an agreement to contribute $531 million to the Large Hadron Collider (LHC) project. Martha Krebs, Director of the Office of Energy Research (DOE) and Bob Eisenstein, Assistant Director of Physical and Mathematical Science at the National Science Foundation sign on behalf of the US, and CERN Director-General Christopher Llewellyn Smith signs on behalf of the laboratory. At the same meeting, the US is granted observer status at CERN.

The Monopole and Exotics Detector at the LHC proposes to build a detector to search for highly ionizing particles and slow exotic decays at the LHC. The letter of intent marks the first official use of the name MoEDAL. It will be the LHC’s seventh detector. Read the MoEDAL letter of intent

As construction workers are preparing the work site for the CMS-detector cavern, they unearth 4th century Gallo-Roman ruins. The find delays work for 6 months while archaeologists excavate the site.  The archaeologists find a Gallo-Roman villa with surrounding fields, as well as coins from Ostia (a seaport of Rome), Lyons in France (then Gaul) and London.    

LHCb is the fourth experiment approved for the LHC. The experiment will study the phenomenon known as CP violation, which would help to explain why matter dominates antimatter in the universe.

A digger removes the final sods of earth from the sides of the cavern that will house the ATLAS detector. 

Construction workers use a modified cement truck on stilts to reinforce the floor of the ATLAS cavern. 

After three years of work, the ATLAS detector cavern (35 x 55 x 40 metres) is fully excavated and completed. CERN officials and dignitaries celebrate the first new LHC cavern on 4 June 2003, complete with an alpinhorn player.

The LHC forward collaboration proposes to build two small calorimeters near the ATLAS detector for high-energy cosmic ray research. Read the LHCf letter of intent

After six and a half years of work, CERN leaders and dignitaries celebrate the completion of a second detector cavern. The CMS cavern is 53 x 27 x 24 metres. To make space for the enormous detector, 250,000 cubic metres of soil have been removed from the detector cavern and a second space that houses technical components.

The last superconducting magnet is lowered down an access shaft to the LHC. The 15-metre dipoles, each weighing 35 tonnes, are the most complex components of the machine. In total, 1232 dipoles were lowered to 50 metres below the surface via a special oval shaft. They were then taken through a transfer tunnel to their final destination in the LHC tunnel, carried by a specially designed vehicle travelling at 3 kilometres per hour.

A component known as a small wheel is the last large piece of the ATLAS detector to be lowered into the cavern. The ATLAS detector has the largest volume of any detector ever constructed.

The pixel detector barrel is the last large piece of the CMS detector to be lowered into the cavern. 

At 10.28am on 10 September 2008 a beam of protons is successfully steered around the 27-kilometre Large Hadron Collider (LHC) for the first time. The machine is ready to embark on a new era of discovery at the high-energy frontier. LHC experiments address questions such as what gives matter its mass, what the invisible 96% of the universe is made of, why nature prefers matter to antimatter and how matter evolved from the first instants of the universe’s existence. Explore the resources prepared for press.

On 19 September 2008, during powering tests of the main dipole circuit in Sector 3-4 of the LHC, a fault occurs in the electrical bus connection in the region between a dipole and a quadrupole, resulting in mechanical damage and release of helium from the magnet cold mass into the tunnel. Proper safety procedures are in force, the safety systems perform as expected, and no-one is put at risk. More about the incident:  A full technical analysis of the incident is available here.  Or read an analysis of the LHC incident on CERN's press office website. 

In line with Japanese tradition, this Daruma doll was painted with one eye to mark the start of the LHC project. The Japanese Vice Minister of Education, Culture, Sports, Science and Technology T. Yamauchi adds the second eye to mark the completion of the project. 

The 53rd and final replacement magnet for the Large Hadron Collider (LHC) is lowered into the accelerator tunnel, marking the end of repair work above ground following the incident in September the year before that brought LHC operations to a halt. The final magnet, a quadrupole designed to focus the beam, is lowered in the afternoon and starts its journey to Sector 3-4, the scene of the September incident. In total 53 magnets were removed from Sector 3-4 after the incident. Sixteen that sustained minimal damage were refurbished and put back into the tunnel. The remaining 37 were replaced and will be refurbished to provide spares for the future.

From a CERN press release, dated 20 November 2009:  Particle beams are once again circulating in the world’s most powerful particle accelerator, CERN’s Large Hadron Collider (LHC). This news comes after the machine was handed over for operation on Wednesday morning. A clockwise circulating beam was established at ten o'clock this evening. This is an important milestone on the road towards first physics at the LHC, expected in 2010. “It’s great to see beam circulating in the LHC again,” said CERN Director General Rolf Heuer. “We’ve still got some way to go before physics can begin, but with this milestone we’re well on the way.” The LHC circulated its first beams on 10 September 2008, but suffered a serious malfunction nine days later. A failure in an electrical connection led to serious damage, and CERN has spent over a year repairing and consolidating the machine to ensure that such an incident cannot happen again. “The LHC is a far better understood machine than it was a year ago,” said CERN’s Director for Accelerators, Steve Myers. “We’ve learned from our experience, and engineered the technology that allows us to move on. That’s how progress is made.” Recommissioning the LHC began in the summer, and successive milestones have regularly been passed since then. The LHC reached its operating temperature of 1.9 Kelvin, or about -271 Celsius, on 8 October. Particles were injected on 23 October, but not circulated. A beam was steered through three octants of the machine on 7 November, and circulating beams have now been re-established. The next important milestone will be low-energy collisions, expected in about a week from now. These will give the experimental collaborations their first collision data, enabling important calibration work to be carried out. This is significant, since up to now, all the data they have recorded comes from cosmic rays. Ramping the beams to high energy will follow in preparation for collisions at 7 TeV (3.5 TeV per beam) next year. Particle physics is a global endeavour, and CERN has received support from around the world in getting the LHC up and running again. “It’s been a herculean effort to get to where we are today,” said Myers. “I’d like to thank all those who have taken part, from CERN and from our partner institutions around the world.”

On 16 December 2009, the LHC ends its first full period of operation. Collisions at 2.36 TeV set a new world record and bring to a close a successful first run for the world’s most powerful particle accelerator. The LHC is put into standby mode for a short technical stop to prepare for higher energy collisions and the start of the main research programme. Over the 2009 run, each of the LHC’s four major experiments, ALICE, ATLAS, CMS and LHCb have recorded over one million particle collisions, which are distributed for analysis around the world on the LHC computing grid. 

After a short technical stop, beams circulate again on 28 February 2010. On 19 March 2010, two 3.5 TeV proton beams successfully circulate in the Large Hadron Collider for the first time. This is the highest energy yet achieved in a particle accelerator and an important step on the way to the start of the LHC research programme. 

ATLAS records collisions at 7 TeV centre-of-mass energy for the first time. Particle physicists around the world anticipate a rich harvest of new physics as the LHC begins its first long run at an energy three and a half times higher than previously achieved at a particle accelerator. Explore the resources prepared for press.

On 18 October 2011, the grand total of data delivered by the LHC during the year reaches almost six inverse femtobarns. At the beginning of the year’s run, the objective for the LHC was to deliver a quantity of data known to physicists as one inverse femtobarn – approximately 100 trillion (102) proton-proton collisions - during the course of 2011. The first inverse femtobarn came on 17 June, setting the experiments up well for the major physics conferences of the summer and requiring the 2011 data objective to be revised upwards to five inverse femtobarns. This milestone is passed on 18 October. “At the end of this year’s proton running, the LHC is reaching cruising speed,” says CERN’s Director for Accelerators and Technology, Steve Myers. “To put things in context, the present data production rate is a factor of 4 million higher than in the first run in 2010 and a factor of 30 higher than at the beginning of 2011.”

In a seminar today the ATLAS and CMS experiments present the status of their searches for the Standard Model Higgs boson. Their results are based on the analysis of considerably more data than those presented at the summer conferences, enough to make significant progress in the search for the Higgs boson, but not enough to make any conclusive statement on the existence or non-existence of the elusive Higgs. The main conclusion is that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 116-130 GeV by the ATLAS experiment, and 115-127 GeV by CMS. Tantalising hints were seen by both experiments in this mass region, but they were not yet strong enough to claim a discovery.

(image: event recorded with the CMS detector in 2012 at a proton-proton centre of mass energy of 8TeV) On 5 April 2012, LHC physics data taking gets underway at a new record collision energy of 8TeV. The LHC declares "stable beams" as two 4 TeV proton beams are brought into collision at the LHC’s four interaction points. This signals the start of physics data taking by the LHC experiments for 2012.  The collision energy of 8 TeV is a new world record, and increases the machine’s discovery potential considerably. “The experience of two good years of running at 3.5 TeV per beam gave us the confidence to increase the energy for this year without any significant risk to the machine,” says CERN’s Director for Accelerators and Technology, Steve Myers. “Now it’s over to the experiments to make the best of the increased discovery potential we’re delivering them!” Although the increase in collision energy is relatively modest, it translates to an increased discovery potential that can be several times higher for certain hypothetical particles. Some such particles, for example those predicted by supersymmetry, would be produced much more copiously at the higher energy. Supersymmetry is a theory in particle physics that goes beyond the current Standard Model, and could account for the dark matter of the universe.

On 4 July 2012, as a curtain raiser to the year’s major particle physics conference, ICHEP 2012 in Melbourne, the ATLAS and CMS experiments present their latest preliminary results in the search for the long-sought Higgs particle. Both experiments have observed a new particle in the mass region around 125-126 GeV.  The next step is to determine the precise nature of the particle and its significance for our understanding of the universe. Are its properties as expected for the long-sought Higgs boson, the final missing ingredient in the Standard Model of particle physics? Or is it something more exotic? The Standard Model describes the fundamental particles from which we, and every visible thing in the universe, are made, and the forces acting between them. All the matter that we can see, however, appears to be no more than about 4% of the total. A more exotic version of the Higgs particle could be a bridge to understanding the 96% of the universe that remains obscure. Explore the resources prepared for press.

On Saturday 16 February at 8.25am the shift crew in the CERN Control Centre extract the beams from the Large Hadron Collider (LHC) for the last time before the machine's first Long Shutdown. The following message marks the event on LHC Page 1: "No beam for a while. Access required: Time estimate ~2 years." January's proton-lead run was followed last week by four days of proton-proton collisions at 1.38 TeV. Final proton collisions in the LHC took place on Thursday at 7.24am, but beams were kept in the machine for 48 hours for "quench tests" on the magnets. A quench is when a superconducting magnet fails to maintain a superconducting state, and therefore stops operating correctly. This can happen if a tiny amount of the beam is off orbit and deposits energy in the magnets. The tests aim to establish what beam loss is actually required to quench the magnets. The LHC’s first run saw major advances in physics, including the discovery of a new particle that looks increasingly like the long–sought Higgs boson, announced on 4 July 2012. And during the last weeks of the run, the remarkable figure of 100 petabytes of data stored in the CERN mass-storage systems was surpassed. This data volume is roughly equivalent to 700 years of full HD-quality movies. The LHC now enters its two-year shutdown, which will see a hive of maintenance activity on all of CERN's accelerators. Work on the LHC will include the consolidation of more than 10,000 interconnections between magnets. The entire ventilation system for the 628-metre circumference Proton Synchrotron will be replaced, as will over 100 kilometres of cables on the Super Proton Synchrotron. The LHC is scheduled to resume in 2015.

François Englert (left) and Peter Higgs at CERN on 4 July 2012, on the occasion of the announcement of the discovery of a Higgs boson by the ATLAS and CMS experiments (Image: Maximilien Brice/CERN)   On 8 October 2013, CERN congratulates François Englert and Peter W. Higgs on the award of the Nobel Prize in physics “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.” The Brout-Englert-Higgs (BEH) mechanism was first proposed in 1964 in two independently published papers: the first by Belgian physicists Robert Brout and François Englert, and the second by British physicist Peter Higgs. It explains how the force responsible for beta decay is much weaker than electromagnetism, but is better known as the mechanism that endows fundamental particles with mass. A third paper, published by Americans Gerald Guralnik and Carl Hagen with their British colleague Tom Kibble further contributed to the development of the new idea, which now forms an essential part of the Standard Model of particle physics. As was pointed out by Higgs, a key prediction of the idea is the existence of a massive boson of a new type, which was discovered by the ATLAS and CMS experiments at CERN in 2012.

Run 2 of the LHC follows a 2-year technical stop that prepared the machine for running at almost double the energy of the LHC’s first run, producing 13 TeV collisions, an energy never achieved by any accelerator in the past.

Published in Nature, the CMS and LHCb collaborations describe the first observation of the very rare decay of the B0s particle into two muon particles. The Standard Model, the theory that best describes the world of particles, predicts that this rare subatomic process happens about four times out of a billion decays, but it has never been seen before. These decays are studied as they could open a window to theories beyond the Standard Model, such as supersymmetry. The analysis is based on data taken at the Large Hadron Collider (LHC) in 2011 and 2012. These data also contain early hints of a similar, but even more rare decay into two muons of the B0, a cousin of the B0s. The B0s and B0 are mesons, in other words, non-elementary unstable subatomic particles composed of a quark and an antiquark, bound together by the strong interaction. Such particles are produced only in high-energy collisions – at particle accelerators, or in nature, for example in cosmic-ray interactions. Explore resources for media. 

From an update on the CERN website:  The Large Hadron Collider (LHC) started delivering physics data today for the first time in 27 months. After an almost two year shutdown and several months re-commissioning, the LHC is now providing collisions to all of its experiments at the unprecedented energy of 13 TeV, almost double the collision energy of its first run. This marks the start of season 2 at the LHC, opening the way to new discoveries. The LHC will now run round the clock for the next three years. “With the LHC back in the collision-production mode, we celebrate the end of two months of beam commissioning,” said CERN Director of Accelerators and Technology Frédérick Bordry. “It is a great accomplishment and a rewarding moment for all of the teams involved in the work performed during the long shutdown of the LHC, in the powering tests and in the beam commissioning process. All these people have dedicated so much of their time to making this happen.” Today at 10.40am, the LHC operators declared “stable beams”, the signal for the LHC experiments that they can start taking data. Beams are made of “trains” of proton bunches moving at almost the speed of light around the 27 kilometre ring of the LHC. These so-called bunch trains circulate in opposite directions, guided by powerful superconducting magnets. Today the LHC was filled with 6 bunches each containing around 100 billion protons. This rate will be progressively increased as the run goes on to 2808 bunches per beam, allowing the LHC to produce up to 1 billion collisions per second. For more information see the live blog that covered events as they unfolded. See a gallery of images from the day. Added 5 June:  Watch a recording of the webcast from the day Webcast: Q & A session

In a paper published by the journal JHEP, the MoEDAL experiment at CERN narrows the window of where to search for a hypothetical particle, the magnetic monopole. Such particles were first predicted by physicist Paul Dirac in the 1930s, but have never been observed so far. Just as electricity comes with two charges, positive and negative, so magnetism comes with two poles, North and South. The difference is that while it’s easy to isolate a positive or negative electric charge, nobody has ever seen a solitary magnetic charge, or monopole. If you take a bar magnet and cut it in half, you end up with two smaller bar magnets, each with a North and South pole. Yet theory suggests that magnetism could be a property of elementary particles. So just as electrons carry negative electric charge and protons carry positive charge, so magnetic monopoles could in theory carry a North or a South pole. If monopoles exist, they are believed to be very massive. As the LHC produces collisions at unprecedented energy, physicists may be able to observe such particles if they are light enough to be in the LHC’s reach. For instance, high-energy photon–photon interactions could produce pairs of North and South monopoles. Monopoles could manifest their presence via their magnetic charge and through their very high ionizing power, estimated to be about 4700 times higher than that of the protons. The MoEDAL experiment at the LHC is designed specifically to look at these effects. Although showing no evidence for trapped monopoles, the results have allowed the MoEDAL collaboration to place new mass limits, assuming a simple production mode of these hypothetical particles. 

In a paper published in Nature Physics, the ALICE collaboration reports that proton collisions sometimes present similar patterns to those observed in the collisions of heavy nuclei. This behaviour was spotted through observation of so-called strange hadrons in certain proton collisions in which a large number of particles are created. Strange hadrons are well-known particles with names such as Kaon, Lambda, Xi and Omega, all containing at least one so-called strange quark. The observed ‘enhanced production of strange particles’ is a familiar feature of quark-gluon plasma, a very hot and dense state of matter that existed just a few millionths of a second after the Big Bang, and is commonly created in collisions of heavy nuclei. But it is the first time ever that such a phenomenon is unambiguously observed in the rare proton collisions in which many particles are created.  “We are very excited about this discovery,” said Federico Antinori, Spokesperson of the ALICE collaboration. “We are again learning a lot about this primordial state of matter. Being able to isolate the quark-gluon-plasma-like phenomena in a smaller and simpler system, such as the collision between two protons, opens up an entirely new dimension for the study of the properties of the fundamental state that our universe emerged from.” The study of the quark-gluon plasma provides a way to investigate the properties of strong interaction, one of the four known fundamental forces, while enhanced strangeness production is a manifestation of this state of matter. The quark-gluon plasma is produced at sufficiently high temperature and energy density, when ordinary matter undergoes a transition to a phase in which quarks and gluons become ‘free’ and are thus no longer confined within hadrons. These conditions can be obtained at the Large Hadron Collider by colliding heavy nuclei at high energy. Strange quarks are heavier than the quarks composing normal matter, and typically harder to produce. But this changes in presence of the high energy density of the quark-gluon plasma, which rebalances the creation of strange quarks relative to non-strange ones. This phenomenon may now have been observed within proton collisions as well. In particular, the new results show that the production rate of these strange hadrons increases with the ‘multiplicity’ – the number of particles produced in a given collision – faster than that of other particles generated in the same collision. While the structure of the proton does not include strange quarks, data also show that the higher the number of strange quarks contained in the induced hadron, the stronger is the increase of its production rate. No dependence on the collision energy or the mass of the generated particles is observed, demonstrating that the observed phenomenon is related to the strange quark content of the particles produced. Strangeness production is in practice determined by counting the number of strange particles produced in a given collision, and calculating the ratio of strange to non-strange particles. Explore resources for media.

At the EPS Conference on High Energy Physics in Venice, the LHCb experiment reports the observation of Ξcc++  (Xicc++), a new particle containing two charm quarks and one up quark. The existence of this particle from the baryon family was expected by current theories, but physicists were looking for such baryons with two heavy quarks for many years. The mass of the newly identified particle is about 3621 MeV, which is almost four times heavier than the most familiar baryon, the proton, a property that arises from its doubly charmed quark content. It is the first time that such a particle has been unambiguously detected. Nearly all the matter that we see around us is made of baryons, which are common particles composed of three quarks, the best-known being protons and neutrons. But there are six types of existing quarks, and theoretically many different potential combinations could form other kinds of baryons. Baryons so far observed are all made of, at most, one heavy quark. “Finding a doubly heavy-quark baryon is of great interest as it will provide a unique tool to further probe quantum chromodynamics, the theory that describes the strong interaction, one of the four fundamental forces,” said Giovanni Passaleva, Spokesperson of the LHCb collaboration. “Such particles will thus help us improve the predictive power of our theories.” “In contrast to other baryons, in which the three quarks perform an elaborate dance around each other, a doubly heavy baryon is expected to act like a planetary system, where the two heavy quarks play the role of heavy stars orbiting one around the other, with the lighter quark orbiting around this binary system,” added Guy Wilkinson, former Spokesperson of the collaboration. Explore resources for the media.