Large Hadron Collider

Large Hadron Collider
(LHC)
LHC.svg
LHC experiments
ATLAS A Toroidal LHC Apparatus
CMS Compact Muon Solenoid
LHCb LHC-beauty
ALICE A Large Ion Collider Experiment
TOTEM Total Cross Section, Elastic Scattering and Diffraction Dissociation
LHCf LHC-forward
LHC preaccelerators
p and Pb Linear accelerators for protons (Linac 2) and Lead (Linac 3)
(not marked) Proton Synchrotron Booster
PS Proton Synchrotron
SPS Super Proton Synchrotron

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator, intended to collide opposing beams of protons or lead ions, each moving at approximately 99.999999% of the speed of light.[1]

The Large Hadron Collider was built by the European Organization for Nuclear Research (CERN) with the intention of testing various predictions of high-energy physics, including the existence of the hypothesised Higgs boson[2] and of the large family of new particles predicted by supersymmetry.[3] 27 kilometres (17 mi) in circumference, it lies underneath the Franco-Swiss border between the Jura Mountains and the Alps near Geneva, Switzerland. It is funded by and built in collaboration with over 10,000 scientists and engineers from over 100 countries as well as hundreds of universities and laboratories.[4]

On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the first time.[5] On 19 September 2008, the operations were halted due to a serious fault between two superconducting bending magnets.[6] The LHC will not be operational again until summer 2009.[7][8]

The LHC was officially inaugurated on 21 October 2008,[9] in the presence of political leaders, science ministers from CERN's 20 Member States, CERN officials, and members of the worldwide scientific community.[10]

Contents

Purpose

A simulated event in the CMS detector, featuring the appearance of the Higgs boson.
A 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.

It is theorised that the collider will produce the elusive Higgs boson, the last unobserved particle among those predicted by the Standard Model. The verification of the existence of the Higgs boson would shed light on the mechanism of electroweak symmetry breaking, through which the particles of the Standard Model are thought to acquire their mass. In addition to the Higgs boson, new particles predicted by possible extensions of the Standard Model might be produced at the LHC. More generally, physicists hope that the LHC will enhance their ability to answer the following questions:[11]

Of the possible discoveries the LHC might make, only the discovery of the Higgs particle is relatively uncontroversial, but even this is not considered a certainty. Stephen Hawking said in a BBC interview that "I think it will be much more exciting if we don't find the Higgs. That will show something is wrong, and we need to think again. I have a bet of one hundred dollars that we won't find the Higgs." In the same interview Hawking mentions the possibility of finding superpartners and adds that "whatever the LHC finds, or fails to find, the results will tell us a lot about the structure of the universe."[14]

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 program. While lighter ions are considered as well, the baseline scheme deals with lead ions.[15] (see A Large Ion Collider Experiment). This will allow an advancement in the experimental program currently in progress at the Relativistic Heavy Ion Collider (RHIC). The aim of the heavy-ion program is to provide a window on a state of matter known as Quark-gluon plasma, which characterized the early stage of the life of the Universe.

Design

Map of the Large Hadron Collider at CERN

The LHC is the world's largest and highest-energy particle accelerator.[16][17] 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 m wide concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the Large Electron-Positron Collider.[18] It crosses the border between Switzerland and France at four points, with most of it in France. Surface buildings hold ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.

The collider tunnel contains two adjacent parallel beam pipes that intersect at four points, each containing a proton beam, which travel in opposite directions around the ring. Some 1,232 dipole magnets keep the beams on their circular path, while an additional 392 quadrupole magnets are used to keep the beams focused, in order to maximize the chances of interaction between the particles in the four intersection points, where the two beams will cross. In total, over 1,600 superconducting magnets are installed, with most weighing over 27 tonnes. Approximately 96 tonnes of liquid helium is needed to keep the magnets at their operating temperature of 1.9 K, 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 protons will take place.

Once or twice a day, as the protons are accelerated from 450 GeV to 7 TeV, the field of the superconducting dipole magnets will be increased from 0.54 to 8.3 tesla (T). The protons will each have an energy of 7 TeV, giving a total collision energy of 14 TeV (2.2 μJ). At this energy the protons have a Lorentz factor of about 7,500 and move at about 99.9999991% of the speed of light. It will take less than 90 microsecond (μs) for a proton to travel once around the main ring – a speed of about 11,000 revolutions per second. Rather than continuous beams, the protons will be bunched together, into 2,808 bunches, so that interactions between the two beams will take place at discrete intervals never shorter than 25 nanoseconds (ns) apart. However it will be operated with fewer bunches when it is first commissioned, giving it a bunch crossing interval of 75 ns.[19]

Prior to being injected into the main accelerator, the particles are prepared by a series of systems that successively increase their energy. The first system is the linear particle accelerator LINAC 2 generating 50 MeV protons, which feeds the Proton Synchrotron Booster (PSB). There the protons are accelerated to 1.4 GeV and injected into the Proton Synchrotron (PS), where they are accelerated to 26 GeV. Finally the Super Proton Synchrotron (SPS) is used to further increase their energy to 450 GeV before they are at last injected (over a period of 20 minutes) into the main ring. Here the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak 7 TeV energy, and finally circulated for 10 to 24 hours while collisions occur at the four intersection points.[20]

CMS detector for LHC

The LHC will also be used to collide lead (Pb) heavy ions 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 PS and SPS before being injected into LHC ring, where they will reach an energy of 2.76 TeV per nucleon.

Detectors

The Large Hadron Collider's (LHC) CMS detectors being installed.

Six detectors have been 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.[17] A Large Ion Collider Experiment (ALICE) and LHCb have more specific roles and the last two TOTEM and LHCf are very much smaller and are for very specialized research. The BBC's summary of the main detectors is:[21]

Test timeline

The first beam was circulated through the collider on the morning of 10 September 2008.[22] 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.[23] The LHC successfully completed its first major test: after a series of trial runs, two white dots flashed on a computer screen showing the protons traveled the full length of the collider. It took less than one hour to guide the stream of particles around its inaugural circuit.[24] CERN next successfully sent a beam of protons in a counterclockwise direction, taking slightly longer at one and a half hours due to a problem with the cryogenics, with the full circuit being completed at 14:59.

On 19 September 2008, a quench occurred in about 100 bending magnets in sectors 3-4, causing loss of approximately six tonnes of liquid helium, which was vented into the tunnel, and a temperature rise of about 100 kelvins in some of the affected magnets. Vacuum conditions in the beam pipe were also lost.[25] Shortly after the incident CERN reported that the most likely cause of the problem was a faulty electrical connection between two magnets, and that - due to the time needed to warm up the affected sectors and then cool them back down to operating temperature - it would take at least two months to fix it.[26] On 16 October 2008 CERN released an analysis of the incident, confirming that it was indeed caused by a faulty electrical connection.[27] At most 29 magnets have been damaged in the incident and will have to be repaired or replaced during the winter shutdown.

In the original timeline of the LHC commissioning, the first "modest" high-energy collisions at a center-of-mass energy of 900 GeV were expected to take place before the end of September 2008, and the LHC was expected to be operating at 10 TeV by the time of the official inauguration on 21 October 2008.[28] However, due to the delay caused by the above-mentioned incident, the collider will not be operational again until summer 2009.[8]

Expected results

Once the supercollider is up and running, CERN scientists estimate that if the Standard Model is correct, a single Higgs boson may be produced every few hours. At this rate, it may take up to three years to collect enough data unambiguously to discover the Higgs boson. Similarly, it may take one year or more before sufficient results concerning supersymmetric particles have been gathered to draw meaningful conclusions.[16]

Proposed upgrade

Main article: Super Large Hadron Collider

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,[29] 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 total cost of the project is expected to be €3.2–6.4 billion.[17] The construction of LHC was approved in 1995 with a budget of 2.6 billion Swiss francs (€1.6 billion), with another 210 million francs (€140 million) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (€300 million) for the accelerator, and 50 million francs (€30 million) for the experiments, along with a reduction in CERN's budget, pushed the completion date from 2005 to April 2007.[30] The superconducting magnets were responsible for 180 million francs (€120 million) of the cost increase. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid, in part due to faulty parts loaned to CERN by fellow laboratories Argonne National Laboratory, Fermilab, and KEK.[31]

David King, the former Chief Scientific Officer for the United Kingdom, has criticised the LHC for taking a higher priority for funds than solving the Earth's major challenges; principally climate change, but also population growth and poverty in Africa.[32]

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, enabling data transfer from CERN to academic institutions around the world.

The Open Science Grid is used as the primary infrastructure in the United States, and also as part of an interoperable federation with the LHC Computing Grid.

The distributed computing project LHC@home was started to support the construction and calibration of the LHC. The project uses the BOINC platform, enabling anybody with an internet connection to use their computer idle time to simulate how particles will travel in the tunnel. With this information, the scientists will be able to determine how the magnets should be calibrated to gain the most stable "orbit" of the beams in the ring.

Safety of particle collisions

Main article: Safety of particle collisions at the Large Hadron Collider

The upcoming experiments at the Large Hadron Collider have sparked fears among the public that the LHC particle collisions might produce doomsday phenomena, involving the production of stable microscopic black holes or the creation of hypothetical particles called strangelets.[33] Two CERN-commissioned safety reviews have examined these concerns and concluded that the experiments at the LHC present no danger and that there is no reason for concern,[34][35][36] a conclusion expressly endorsed by the American Physical Society, the world's second largest organization of physicists.[37]

Operational challenges

The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of the huge energy stored in the magnets and the beams.[20][38] While operating, the total energy stored in the magnets is 10 GJ (equivalent to one and a half barrels of oil or 2.4 tons of TNT) and the total energy carried by the two beams reaches 724 MJ (about a tenth of a barrel of oil, or half a lightning bolt).[39]

Loss of only one ten-millionth part (10−7) of the beam is sufficient to quench a superconducting magnet, while the beam dump must absorb 362 MJ, an energy equivalent to that of burning eight kilograms of oil, for each of the two beams. These immense energies are even more impressive considering how little matter is carrying it: 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 fine sand.

On 10 August 2008, computer hackers defaced a website at CERN, criticizing their computer security. There was no access to the control network of the collider.[40][41]

Construction accidents and delays

In popular culture

The Large Hadron Collider was featured in Angels & Demons by Dan Brown, which involves dangerous antimatter created at the LHC being used as a weapon against the Vatican. CERN published a "Fact or Fiction?" page discussing the accuracy of the book's portrayal of the LHC, CERN, and particle physics in general.[48] 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.[49]

CERN employee Katherine McAlpine's "Large Hadron Rap"[50] surpassed three million YouTube views on 15 September 2008.[51][52][53]

BBC Radio 4 commemorated the switch-on of the LHC on 10 September 2008 with "Big Bang Day".[54] Included in this event was a radio episode of the TV series Torchwood, with a plot involving the LHC, entitled Lost Souls.[55] CERN's director of communications, James Gillies, commented, "The CERN of reality bears little resemblance to that of Joseph Lidster's Torchwood script."[56]

The LHC plays a major role in the science fiction novel Flashforward by Robert J. Sawyer. As the first ion collisions occur in the ALICE detector everyone in the world experiences a two-minute 'flashforward' to a time twenty one years ahead. The novel, which received the Aurora Award in 1999, follows the efforts of CERN scientists to provide an explanation for the event and deal with the human problems presented by knowledge of the future. A TV adaptation is being developed by ABC.[57]

In the Stargate: Atlantis episode Brain Storm, one of the main characters refers to the Hadron Collider as an example of a source of unnecessary paranoia in respect to a scientific experiment going wrong

References

  1. ↑ "How Fast do These Protons Go?". yogiblog. Retrieved on 2008-10-29.
  2. ↑ "CERN - Missing Higgs". CERN. Retrieved on 2008-10-10.
  3. ↑ "CERN - Towards a superforce". CERN. Retrieved on 2008-10-10.
  4. ↑ "Large Hadron Collider: thirteen ways to change the world". Telegraph (16 September 2008). Retrieved on 2008-10-10.
  5. ↑ "First beam in the LHC - accelerating science". CERN Press Office (10 September 2008). Retrieved on 2008-10-09.
  6. ↑ "Collider halted until next year". BBC News (23 September 2008). Retrieved on 2008-10-09.
  7. ↑ "Large Hadron Collider to remain shut until middle of next year". Times Online (17 November 2008). Retrieved on 2008-18-11.
  8. ↑ 8.0 8.1 8.2 Tom Espiner (30 november 2008). "A longer delay for the Large Hadron Collider". CNET news.
  9. ↑ "CERN inaugurates the LHC". CERN Press Office (21 October 2008). Retrieved on 2008-10-21.
  10. ↑ ap.google.com, Sidelined CERN collider gets a new, formal sendoff
  11. ↑ Greene, Brian (September 11, 2008). "The Origins of the Universe: A Crash Course". The New York Times.
  12. ↑ "...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
  13. ↑ Randall, Lisa. "Extra Dimensions and Warped Geometries. Science. Vol. 296, 23 May 2002]" (PDF).
  14. ↑ Stephen Hawking interviewed by the BBC on the switch-on of the Large Hadron Collider. news.bbc.co.uk. Retrieved on 10 September 2008.
  15. ↑ "Ions for LHC".
  16. ↑ 16.0 16.1 CERN Communication Group (January 2008). "CERN FAQ — LHC: the guide" (PDF) 44. Geneva: CERN. Retrieved on 2008-09-12.
  17. ↑ 17.0 17.1 17.2 Achenbach, Joel (2008-03-01). "The God Particle". National Geographic Magazine (National Geographic Society). ISSN 0027-9358. http://ngm.nationalgeographic.com/2008/03/god-particle/achenbach-text. Retrieved on 2008-02-25. 
  18. ↑ "The Z factory". European Organization for Nuclear Research.
  19. ↑ "LHC commissioning with beam". CERN.
  20. ↑ 20.0 20.1 Operational challenges of the LHC. 53 Microsoft PowerPoint slides.
  21. ↑ Paul Rincon (9 September 2008). "Cern collider ready for power-up". BBC. Retrieved on 2008-09-09.
  22. ↑ "Success for 'Big Bang' experiment". BBC.
  23. ↑ "First beam in the LHC - accelerating science". CERN. Retrieved on 2008-09-10.
  24. ↑ "Scientists cheer as protons complete first circuit of Large Hadron Collider". Times Online. Retrieved on 2008-10-06.
  25. ↑ "Interim Summary Report on the Analysis of the 19 September 2008 Incident at the LHC" (PDF). CERN.
  26. ↑ "Incident in LHC sector 3-4". CERN.
  27. ↑ "CERN releases analysis of LHC incident". CERN.
  28. ↑ Henderson, Mark (18 September 2008) "‘Big bang machine’ is back on collision course after its glitches are fixed". Times Online.
  29. ↑ "PDF presentation of proposed LHC upgrade" (PDF).
  30. ↑ Maiani, Luciano (16 October 2001). "LHC Cost Review to Completion". CERN. Retrieved on 2001-01-15.
  31. ↑ Feder, Toni (December 2001). "CERN Grapples with LHC Cost Hike". Physics Today 54 (12): 21. doi:10.1063/1.1445534. http://www.aip.org/pt/vol-54/iss-12/p21b.html. Retrieved on 2007-01-15. 
  32. ↑ Amostitle, Jonathan (8 September 2008). "'Climate crisis' needs brain gain". BBC.
  33. ↑ Boyle, Alan (2 September 2008). "Courts weigh doomsday claims". Cosmic Log. msnbc.com.
  34. ↑ Blaizot JP, Iliopoulos J, Madsen J, Ross GG, Sonderegger P, Specht HJ (2003). Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC (PDF, 176 KiB). CERN. Geneva. CERN-2003-001.
  35. ↑ Ellis J, Giudice G, Mangano ML, Tkachev I, Wiedemann U (LHC Safety Assessment Group) (5 September 2008). "Review of the Safety of LHC Collisions" (PDF, 586 KiB). ''Journal of Physics G: Nuclear and Particle Physics. 35, 115004 (18pp). doi:10.1088/0954-3899/35/11/115004. arXiv:0806.3414. CERN record.
  36. ↑ "The safety of the LHC". CERN 2008 (CERN website).
  37. ↑ "Statement by the Executive Committee of the DPF on the Safety of Collisions at the Large Hadron Collider" issued by the Division of Particles & Fields (DPF) of the American Physical Society (APS)
  38. ↑ "Challenges in accelerator physics".
  39. ↑ "Beam Parameters and Definitions" (PDF).
  40. ↑ http://it-support-servicestatus.web.cern.ch/it-support-servicestatus/IncidentArchive/080915-CMSMON.htm
  41. ↑ Harvey, Mike; & Henderson, Mark (13 September 2008). "Hackers claim there’s a black hole in the atom smashers’ computer network". The Times.
  42. ↑ CERN (26 October 2005). "and French Message from the Director-General". Press release. Retrieved on 2007-01-15.
  43. ↑ "Fermilab'Dumbfounded'by fiasco that broke magnet".
  44. ↑ "LHC Magnet Test Failure".
  45. ↑ "Updates on LHC inner triplet failure".
  46. ↑ "The God Particle". www.bbc.com. Retrieved on 2007-05-22.
  47. ↑ http://news.bbc.co.uk/2/hi/in_depth/7632408.stm
  48. ↑ "Angels and Demons". CERN. Retrieved on 2008-07-16.
  49. ↑ Perkins, Ceri. "ATLAS gets the Hollywood treatment". ATLAS e-News. CERN. Retrieved on 2008-07-16.
  50. ↑ "YouTube - Large Hadron Rap". Youtube.com. Retrieved on 2008-09-09.
  51. ↑ "Large Hadron Rap links and lyrics".
  52. ↑ "Rap about world's largest science experiment becomes YouTube hit". Telegraph. Last Updated: 2 September 2008
  53. ↑ Bogo, Jennifer (1 August 2008). "Large Hadron Collider Rap Teaches Particle Physics in 4 Minutes". Popular Mechanics.
  54. ↑ "BBC - Radio 4 - Big Bang Day". BBC (2008-09-10). Retrieved on 2008-09-11.
  55. ↑ "Programming for Big Bang Day on BBC Radio 4". BBC Press Office. Retrieved on 2008-08-11.
    "Radio 4 - Big Bang Day". BBC. Retrieved on 2008-09-10.
    Donovan, Paul (2008-09-07). "The BBC has Big Bang to rights", The Sunday Times. Retrieved on 2008-09-11. 
  56. ↑ Gillies, James. "CERN in Science-Fiction". BBC Radio 4 website. BBC. Retrieved on 2008-09-11.
  57. ↑ "[http://www.comingsoon.net/news/tvnews.php?id=49023 Flash Forward New Companion for Lost]". www.comingsoon.net. Retrieved on 2008-08-09.
Hadron Colliders
Intersecting Storage Rings CERN, 1971–1984
Super Proton Synchrotron CERN, 1981–1984
ISABELLE BNL, cancelled in 1983
Tevatron Fermilab, 1987–2009
Relativistic Heavy Ion Collider BNL, operational since 2000
Superconducting Super Collider Cancelled in 1993
Large Hadron Collider CERN, 2008–
Very Large Hadron Collider Theoretical

External links

European Organization for Nuclear Research (CERN)
Experiments
1976–1984 Super Proton Synchrotron
UA1 · UA2
Fixed target experiments at the SPS
NA48 · COMPASS
1989–2000 Large Electron-Positron Collider
Aleph · Delphi  · Opal · L3
2008– Large Hadron Collider
ATLAS · CMS · LHCb · TOTEM · LHCf · ALICE
Acceleration Structure
p and Pb · Proton Synchrotron Booster · Proton Synchrotron · Super Proton Synchrotron
Others
LHC@home