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46°14′N 06°03′E / 46.233°N 6.050°E / 46.233; 6.050 The Large Hadron Collider (LHC) is a particle accelerator complex that will collide opposing beams of 7 TeV protons together in order to explore the validity and limitations of the highly successful current theoretical picture for particle physics, the standard model, which is known however to break down at sufficiently high energy. It is being built by the European Organization for Nuclear Research (CERN), and lies under the Franco-Swiss border near Geneva, Switzerland, where it is undergoing commissioning while being cooled down to its final operating temperature of approximately 2K. The first beams are due for injection in August 2008, with the first collisions planned to take place about two months later. The LHC will become the world's largest and highest-energy particle accelerator. The LHC is being funded and built in collaboration with over two thousand physicists from thirty-four countries as well as hundreds of universities and laboratories.

When activated, it is theorized that the collider will produce the elusive Higgs boson, the observation of which could confirm the predictions and "missing links" in the Standard Model of physics and could explain how other elementary particles acquire properties such as mass. The verification of the existence of the Higgs boson would be a significant step in the search for a Grand Unified Theory, which seeks to unify three of the four known fundamental forces: electromagnetism, the strong nuclear force and the weak nuclear force, leaving out only gravity. The Higgs boson may also help to explain why gravitation is so weak compared to the other three forces. In addition to the Higgs boson, other theorized novel particles that might be produced, and for which searches are planned, include strangelets, micro black holes, magnetic monopoles and supersymmetric particles.

Technical design

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 underground. The 3.8 metre diameter, concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the LEP, an electron-positron collider. It crosses the border between Switzerland and France at four points, although most of it is in France. Surface buildings hold ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two adjacent beam pipes, each containing a proton beam (a proton is one type of hadron). The two beams travel in opposite directions around the ring. Some 1232 bending magnets keep the beams on their circular path, while an additional 392 focusing 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 1600 superconducting magnets are installed, with most weighing over 27 tonnes. Approximately 96 tonnes of liquid helium is needed to keep the magnets at the operating temperature, making the LHC the largest cryogenic facility in the world at liquid helium temperature.

The protons will each have an energy of 7 TeV, giving a total collision energy of 14 TeV. It will take less than 90 microseconds for a proton to travel once around the main ring. 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 than 25 ns apart. When the collider is first commissioned, it will be operated with fewer bunches, to give a bunch crossing interval of 75 ns. The number of bunches will later be increased to give a final bunch crossing interval of 25 ns.

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 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 increase their energy to 450 GeV before they are at last injected into the main ring, where proton bunches are accumulated, accelerated to their peak 7 TeV energy, and finally stored for many hours while collisions occur at the four intersection points.

The LHC will also be used to collide lead (Pb) nuclei with a collision energy of 1,150 TeV. The Pb ions will be first accelerated by the linear accelerator Linac 3, and the Low-Energy Injector Ring (LEIR) will be used as an ion storage and cooler unit. The ions then will be further accelerated by the Proton Synchrotron (PS) and Super Proton Synchrotron (SPS) before being injected into LHC ring, where they will reach an energy of 2.76 TeV per nucleon.

Six detectors are being constructed at the LHC, located underground in large caverns excavated at the LHC's intersection points. Two of them, the ATLAS experiment and the Compact Muon Solenoid (CMS), are large, "general purpose" particle detectors. A Large Ion Collider Experiment (ALICE) is designed to study the properties of quark-gluon plasma from the debris of heavy-ion collisions. The other three, (LHCb, TOTEM, and LHCf), are smaller and more specialized. A seventh experiment, FP420 (Forward Physics at 420m), has been proposed which would add detectors to four available spaces located 420m on either side of the ATLAS and CMS detectors.

Research

When in operation, about seven thousand scientists from eighty countries will have access to the LHC, the largest national contingent of seven hundred being from the United States. Physicists hope to use the collider to test various grand unified theories and enhance their ability to answer the following questions:

• Is the popular Higgs mechanism for generating elementary particle masses in the Standard Model realised in nature? If so, how many Higgs bosons are there, and what are their masses?
• Will the more precise measurements of the masses of the quarks continue to be mutually consistent within the Standard Model?
• Do particles have supersymmetric ("SUSY") partners?
• Why are there apparent violations of the symmetry between matter and antimatter? See also CP-violation.
• Are there extra dimensions indicated by theoretical gravitons, as predicted by various models inspired by string theory, and can we "see" them?
• What is the nature of dark matter and dark energy?
• Why is gravity so many orders of magnitude weaker than the other three fundamental forces?

As an ion collider

The LHC physics program 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 (Pb) ions. This will allow an advancement in the experimental programme currently in progress at the Relativistic Heavy Ion Collider (RHIC).

Proposed upgrade

After some years of running, any particle physics experiment typically begins to suffer from diminishing returns; each additional year of operation discovers less than the year before. The way around the diminishing returns is to upgrade the experiment, either in energy or in luminosity.

A luminosity upgrade of the LHC, called the Super LHC, has been proposed, to be made after ten years of LHC operation. The optimal path for the LHC luminosity upgrade includes an increase in the beam current (i.e., the number of protons in the beams) and the modification of the two high luminosity interaction regions, ATLAS and CMS. To achieve these increases, the energy of the beams at the point that they are injected into the (Super) LHC should also be increased to 1 TeV. This will require an upgrade of the full pre-injector system, the needed changes in the Super Proton Synchrotron being the most expensive.

Cost

The construction of LHC was approved in 1995 with a budget of 2.6 billion Swiss francs, with another 210 million francs (€140 M) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (€300 M) for the accelerator, and 50 million francs (€30 M) for the experiments, along with a reduction in CERN's budget, pushed the completion date from 2005 to April 2007. 180 million francs (€120 M) of the cost increase have been due to the superconducting magnets. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid. In part this was due to faulty parts lent to CERN by fellow laboratories Argonne National Laboratory or Fermilab (home to the Tevatron, the world's largest particle accelerator until CERN finishes the Large Hadron Collider). The total cost of the project is anticipated to be between US$5 and US$10 billion.

Computing resources

The LHC Computing Grid is being constructed to handle the massive amounts of data produced by the Large Hadron Collider. It incorporates both private fiber optic cable links and existing high-speed portions of the public Internet, to get data from CERN to academic institutions around the world.

The distributed computing project LHC@home was started to support the construction and calibration of the LHC. The project uses the BOINC platform 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.

Safety issues

Safety of high-energy particle collisions in the LHC

Concerns have been raised regarding the safety of the Large Hadron Collider (LHC) on the grounds that high-energy particle collisions performed in the LHC might produce dangerous phenomena, including micro black holes, strangelets, vacuum bubbles and magnetic monopoles. In response to these concerns, the LHC Safety Study Group, a group of independent scientists, performed a safety analysis of the LHC and concluded in a report published in 2003 that there is "no basis for any conceivable threat". In 2008, drawing from new experimental data and theoretical understanding, the LHC Safety Assessment Group (LSAG) published a report updating the 2003 safety review, in which they reaffirmed and extended its conclusions that LHC particle collisions present no danger, stating that "the LHC will do nothing that nature has not done a million times before". The LSAG report was reviewed and endorsed by CERN’s Scientific Policy Committee (SPC), a group of external scientists that advises CERN’s governing body, its Council.

Legal challenge

On 21 March 2008 a complaint requesting an injunction to halt the LHC's startup was filed by a group of seven concerned individuals against CERN and its American collaborators, the US Department of Energy, the National Science Foundation and the Fermi National Accelerator Laboratory, before the United States District Court for the District of Hawaii.

The plaintiffs include Walter L. Wagner who notably was unable to obtain an injunction against the much lower energy RHIC for similar concerns. The plaintiffs demanded an injunction against the LHC's activation for 4 months after issuance of the LHC Safety Assessment Group's (LSAG) most recent safety documentation, and a permanent injunction until the LHC can be demonstrated to be reasonably safe within industry standards. The US Federal Court scheduled trial to begin June 16, 2009. The LSAG review, issued on 20 June 2008 after outside review, found “... no basis for any concerns about the consequences of new particles or forms of matter that could possibly be produced by the LHC”. The US Government, in response, called for summary dismissal of the suit as against the government defendants as untimely due to the expiration of a six-year statute of limitations, since funding began by 1999 and has essentially been completed already, and also called the hazards claimed by the plaintiffs "overly speculative and not credible". According to a spokesman for the US DOE, the court set Sept 2, 2008 for a hearing on the government's motion to dismiss, with further briefs and depositions expected to be filed by both sides before that date. In the meanwhile, the defendant CERN has defaulted on its appearance in court, and a request for entry of default against CERN is pending. The plaintiffs have until September 24, 2008 to respond to the government's motion to dismiss. First collisions at the LHC are expected in October 2008.

Operational safety

Even at the local level, the size of the LHC constitutes an exceptional engineering challenge with unique safety issues. During operations, the total energy stored in the magnets is 10 GJ, and each of the two beams carries an overall energy that reaches 362 MJ. For comparison, 362 MJ is the kinetic energy of a TGV running at 157 km/h (98 mph), while 724 MJ, the total energy of the two beams, is equivalent to the detonation energy of approximately 173 kilograms (381 lb) of TNT, and 10 GJ is about 2.4 tons of TNT. Loss of only 10 of the beam is sufficient to quench a superconducting magnet, while the beam dump must absorb an energy equivalent to a typical air-dropped bomb. These immense kinetic energies are even more impressive when one considers how little matter is carrying it. Under nominal operating conditions (2808 bunches per beam, 1.15E11 protons per bunch), the beam pipes contain about 1.08E-9 grams of hydrogen, which, in standard conditions for temperature and pressure, would fill a volume of roughly 0.01 mm.

Construction accidents and delays

On October 25, 2005, a technician was killed in the LHC tunnel when a crane load was accidentally dropped.

On March 27, 2007 a cryogenic magnet support broke during a pressure test involving one of the LHC's inner triplet (focusing quadrupole) magnet assemblies, provided by Fermilab and KEK. No one was injured. Fermilab director Pier Oddone stated 'In this case we are dumbfounded that we missed some very simple balance of forces.' This 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 startup date, then planned for November 2007, by several weeks.

LHC in Popular Culture

See Large Hadron Collider in Popular Culture

See also

• Higgs boson
• Higgs mechanism
• International Linear Collider
• LHC Computing Grid
• Particle accelerator
• Standard model

Notes and references

1. ^ D. Overbye, New York Times  June 21, 2008.
2. ^ Achenbach, Joel (2008-03-01). "The God Particle". National Geographic Magazine. National Geographic Society. ISSN 0027-9358. Retrieved 2008-02-25.
3. Ellis, John (19 July 2007). "Beyond the standard model with the LHC". Nature. 448: 297–301. doi:10.1038/nature06079. Retrieved 2007-11-24. There are good reasons to hope that the LHC will find new physics beyond the standard model, but no guarantees. The most one can say for now is that the LHC has the potential to revolutionize particle physics, and that in a few years' time we should know what course this revolution will take.
4. I.F. Ginzburg, A. Schiller, “Search for a heavy magnetic monopole at the Fermilab Tevatron and CERN LHC”, Phys. Rev. D57 (1998) 6599-6603, arXiv:hep-ph/9802310; A. Angelis et al., "Formation of Centauro and Strangelets in Nucleus-Nucleus Collisions at the LHC and their Identification by the ALICE Experiment”, arXiv:hep-ph/9908210; G. L. Alberghi, et al., “Searching for micro black holes at LHC”, IFAE 2006, Incontri di Fisica delle Alte Energie (Italian Meeting on High Energy Physics)
5. T. Lari, "Search for Supersymmetry with early ATLAS data"
6. Symmetry magazine, April 2005
7. "CERN - LEP: the Z factory".
8. LHC Guide booklet
9. LHC commissioning with beam, May 2008
10. "FP420 R&D Project".
11. "...in the public presentations of the aspiration of particle physics we hear too often that the goal of the LHC or a linear collider is to check off the last missing particle of the standard model, this year’s Holy Grail of particle physics, the Higgs boson. The truth is much less boring than that! What we’re trying to accomplish is much more exciting, and asking what the world would have been like without the Higgs mechanism is a way of getting at that excitement." -Chris Quigg, Nature's Greatest Puzzles
12. "Ions for LHC".
13. "PDF presentation of proposed LHC upgrade" (PDF).
14. Maiani, Luciano (16 October 2001). "LHC Cost Review to Completion". CERN. Retrieved 2001-01-15.
15. Feder, Toni (2001). "CERN Grapples with LHC Cost Hike". Physics Today. 54 (12): 21. Retrieved 2007-01-15. {{cite journal}}: Unknown parameter |month= ignored (help)
16. ^ "The safety of the LHC". CERN 2008 (CERN website).
17. Blaizot JP, Iliopoulos J, Madsen J, Ross G, Sonderegger P, Specht H (2003). "Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC". CERN. Geneva. CERN-2003-001.
18. Tiny Black Holes - Physicist Dave Wark of Imperial College, London reporting for NOVA scienceNOW
19. ^ Ellis J, Giudice G, Mangano ML, Tkachev I, Wiedemann U (2008). "Review of the Safety of LHC Collisions". LHC Safety Assessment Group.
20. Giddingsa SB, Mangano ML (2008). "Astrophysical implications of hypothetical stable TeV-scale black holes". CERN. Geneva. CERN-PH-TH/2008-025.
21. CERN Scientific Policy Committee (2008). "SPC Report on LSAG Documents".
22. "Federal District Court Filings and Dockets Hawaii". MSNBC Cosmic Log - Doomsday Fear Sparks Lawsuit
23. "Copy of Complaint and Affidavits at LHCFacts.org".
24. "DOOMSDAY UNDER DEBATE by msnbc Cosmic Log".
25. Government Seeks Dismissal of End-of-World Suit Against Collider, NY Times 27 June 2008
26. Hewett, JoAnne (25 October 2005). "Tragedy at CERN" (Blog). Cosmic Variance. Retrieved 2007-01-15. author and date indicate the beginning of the blog thread
27. "Message from the Director-General" (Press release) (in English and French). CERN. 26 October 2005. Retrieved 2007-01-15.{{cite press release}}: CS1 maint: unrecognized language (link)
28. "Fermilab'Dumbfounded'by fiasco that broke magnet".
29. "LHC Magnet Test Failure".
30. "Updates on LHC inner triplet failure".
31. "The God Particle". www.bbc.com. Retrieved 2007-05-22.

External links

• slashdot.org: Why the LHC Won't Destroy the World
• TED talks (video) - Brian Cox: What really goes on at the Large Hadron Collider
• LHC - The Large Hadron Collider webpage
• Overview of the LHC at CERN's public webpage
• Challenges in accelerator physics
• LHC UK webpage
• US LHC webpage
• UK Science Museum, London Exhibition supported by the Science and Technology Facilities Council
• The Alice experiment
• Compact Muon Solenoid main page
• Compact Muon Solenoid page (U.S. collaboration)
• LCG - The LHC Computing Grid webpage
• The Large Hadron Collider ATLAS Experiment - Virtual Reality (VR) photography panoramas (requires QuickTime)
• LHC startup plan. Includes dates, energies and luminosities
• Seed short film - Lords of the Ring
• 'Super-collider' tunnel nears completion The Independent 1 March 2008
• LHC Defense Fund - Anti-LHC organization

Articles

• Energising the quest for 'big theory'
• symmetry magazine LHC special issue August 2006, special issue December 2007
• BBC Horizon, The six billion dollar experiment
• New Yorker: Crash Course. The world’s largest particle accelerator (ca. 6 500 words)
• NYTimes: A Giant Takes On Physics’ Biggest Questions (ca. 4 300 words)
• Beam Parameters and Definitions. The chapter of the LHC Technical Design Report (TDR) that lists of all the beam parameters for the LHC.
• Large Hadron Collider, Ingenia magazine

• Particle physics facilities
• E-Science
• Large Hadron Collider