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Thursday, September 11, 2008

Large Hadron Collider........................Part 1

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator complex, intended to collide opposing beams of protons charged with very high energy. Its main purpose is to explore the validity and limitations of the Standard Model, the current theoretical picture for particle physics. It is theorized that the collider will confirm the existence of the Higgs boson, the observation of which could confirm the predictions and missing links in the Standard Model, and could explain how other elementary particles acquire properties such as mass.

The LHC was built by the European Organization for Nuclear Research (CERN), and lies underneath the Franco-Swiss border near Geneva, Switzerland. It is funded by and built in collaboration with over eight thousand physicists from over eighty-five countries as well as hundreds of universities and laboratories. The LHC is already operational and is presently in the process of being prepared for collisions. The first beams were circulated through the collider on 10 September 2008, and the first high-energy collisions are planned to take place after the LHC is officially unveiled on 21 October.

Although a few individuals have questioned the safety of the planned experiments in the media and through the courts, the consensus in the scientific community is that there is no conceivable threat from the LHC particle collisions.

Design

The LHC is the world's largest and highest-energy particle accelerator.[1] 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.[2] The 3.8-metre (150 in.) diameter, concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the Large Electron-Positron Collider.[3] Mostly in France, it crosses the border between Switzerland and France at four points. 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.[4]
Superconducting quadrupole electromagnets are used to direct the beams to four intersection points, where interactions between protons will take place.
Superconducting quadrupole electromagnets are used to direct the beams to four intersection points, where interactions between protons will take place.



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

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 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 99.999999% of light speed. It will take less than 90 microseconds 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 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.[5]

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. 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 stored for 10 to 24 hours while collisions occur at the four intersection points.[6]

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

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.[1] "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. The BBC's summary of the detectors is:[7]

ATLAS – one of two so-called general purpose detectors. Atlas will be used to look for signs of new physics, including the origins of mass and extra dimensions.

CMS – the other general purpose detector will, like ATLAS, hunt for the Higgs boson and look for clues to the nature of dark matter.

ALICE – will study a "liquid" form of matter called quark-gluon plasma that existed shortly after the Big Bang.

LHCb – equal amounts of matter and antimatter were created in the Big Bang. LHCb will try to investigate what happened to the "missing" anti-matter.

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

When activated, it is theorized that the collider will produce the elusive Higgs boson. 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 with the other three forces. In addition to the Higgs boson, other theorized particles, models and states might be produced, and for some searches are planned, including supersymmetric particles,[8] compositeness (technicolor),[9] extra dimensions,[10] strangelets,[11] micro black holes and magnetic monopoles.

Research

When in operation, about seven thousand scientists from eighty countries will have access to the LHC. 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?[14]
* 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?[1]
* Why are there apparent violations of the symmetry between matter and antimatter?[1] See also CP-violation.
* Are there extra dimensions, as predicted by various models inspired by string theory, and can we "see" them?
* What is the nature of dark matter and dark energy?[1]
* Why is gravity so many orders of magnitude weaker than the other three fundamental forces?

Renowned British astrophysicist Stephen Hawking has bet against the mega-experiment finding the elusive Higgs particle. "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 $100 that we won't find the Higgs," Hawking speculated, but the experiment could discover superpartners, particles that would be supersymmetric partners to particles already known. "Their existence would be a key confirmation of string theory, and they could make up the mysterious dark matter that holds galaxies together. Whatever the LHC finds, or fails to find, the results will tell us a lot about the structure of the universe," he said.[15]

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 ions.[16] This will allow an advancement in the experimental programme currently in progress at the Relativistic Heavy Ion Collider (RHIC).

Test timeline

September 2008

The first beam was circulated through the collider on the morning of 10 September 2008.[17] 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 am local time.[18] 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.[19] CERN next successfully sent a beam of protons in a counterclockwise direction.

October 2008

The first high-energy collisions are planned to take place after the LHC is officially unveiled on 21 October 2008.[20]

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,[21] 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 anticipated to be €3.2–6.4 billion.[1] 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.[22] 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 and Fermilab.[23]

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.[24]

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 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 particle collisions

Main article: Safety of the Large Hadron Collider

Although some individuals, including scientists, have questioned the safety of the planned experiments in the media and through the courts, the consensus in the scientific community is that there is no basis for any conceivable threat from the LHC particle collisions.[25][26][27]

Operational safety

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.[6][28] While operating, the total energy stored in the magnets is 10 GJ (equivalent to 2.4 tons of TNT) and the total energy carried by the two beams reaches 724 MJ.[29]

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 an energy equivalent to that of a typical air-dropped bomb. 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.

Construction accidents and delays

On 25 October 2005, a technician was killed in the LHC tunnel when a crane load was accidentally dropped.[30] On 27 March 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.[31] 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.[32][33] Repairing the broken magnet and reinforcing the eight identical assemblies used by LHC delayed the startup date,[34] then planned for November 2007, by several weeks.

In popular culture

The Large Hadron Collider has been featured in a number of novels, including Flashforward by Robert J. Sawyer, Black Hole by Angelo Paratico,[35] and Decipher by Stel Pavlou, which described it in some detail. One of the most visible examples is Angels & Demons by Dan Brown, which involves dangerous antimatter created at the LHC 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.[36] The movie version of the book has footage filmed on-site at one of the experiments at the LHC; the director, Ron Howard, also met with CERN experts in an effort to make the science in the story more accurate.[37] CERN employee Katherine McAlpine's "Large Hadron Rap"[38] surpassed two million YouTube views on 10 September 2008.[39][40][41]

BBC Radio 4 broadcast "Big Bang Day" on 10 September 2008 to coincide with the LHC being switched on. Included in this event was a radio episode of the TV series Torchwood, with a plot involving the LHC, entitled Lost Souls.[42][43][44]

On 10 September, to commemorate the firing of the Large Hadron Collider, Google displayed a custom Google Doodle[45] with a drawing of the LHC which linked to a web search for "Large Hadron Collider".

A 16-year-old girl from Sarangpur, Madhya Pradesh, India allegedly committed suicide after watching Indian news channels stating the possibility of Doomsday as the experiment began.[46]

From : Wikipedia

by STEVIE @ 3:44 PM.