The LARGE HADRON COLLIDER

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator complex, intended to collide opposing beams of protons (one of several types of hadrons) with very high kinetic 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. This would supply a crucial missing link in the Standard Model and 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 between the Jura Mountains and the Alps 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 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 expected to take place after 6-8 weeks.

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.

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.

When in operation, about seven thousand scientists from eighty countries will have access to the LHC. It is theorized 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:

1. Is the Higgs mechanism for generating elementary particle masses in the Standard Model indeed realised in nature?

If so, how many Higgs bosons are there, and what are their masses?

2. Are electromagnetism, the strong nuclear force and the weak nuclear force just different manifestations of a single unified force, as predicted by various Grand Unification Theories?

3. Why is gravity so many orders of magnitude weaker than the other three fundamental forces?

4. Is Supersymmetry realised in nature, implying that the known Standard Model particles have supersymmetric partners?

5. Will the more precise measurements of the masses and decays of the quarks continue to be mutually consistent within the Standard Model?

6. Why are there apparent violations of the symmetry between matter and antimatter?

7. What is the nature of dark matter and dark energy?

8. Are there extra dimensions, as predicted by various models inspired by string theory, and can we detect them?

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.

The total cost of the project is expected to be €3.2–6.4 billion.

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.

Once the supercollider is up and running, CERN scientists estimate that if the Standard Model is correct, a Higgs boson may be produced every few hours. At this rate, it may take up to three years to collect enough statistics unambiguously to discover the Higgs boson.

Although there have been questions concerning the safety of the planned experiments in the media and even through the courts, the consensus in the scientific community is that there is no basis for any conceivable threat from the LHC particle collisions.

A primary concern, the appearance of micro black holes, has been dismissed due to the improbability of their production and, even if produced, their infinitesimal size and instantaneous decay.

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