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.
The Large Hadron Collider
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.
(Image: Martin Aleksa, Lyndon Evans, Fabiola Gianotti and Peter Jenni toast running at 7 TeV)
After initial lower energy collision physics from November 2009 onwards, 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.
“It’s a great day to be a particle physicist,” says CERN Director-General Rolf Heuer. “A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends.”
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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.
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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.
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: