The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature.

The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as much as 175 metres (574 ft) beneath the Franco-Swiss border near Geneva, Switzerland. This synchrotron is designed to collide opposing particle beams of either protons at an energy of 7 teraelectronvolts (7 TeV or 1.12 microjoules) per particle, or lead nuclei at an energy of 574 TeV (92.0 µJ) per nucleus.^[1][2] The term hadron refers to particles composed of quarks.

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 hypothesized Higgs boson^[3] and of the large family of new particles predicted by supersymmetry.^[4] It was built in collaboration with over 10,000 scientists and engineers from over 100 countries, as well as hundreds of universities and laboratories.^[5]

On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the first time,^[6] but 9 days later operations were halted due to a serious fault.^[7] On 20 November 2009 they were successfully circulated again,^[8] with the first recorded proton–proton collisions occurring 3 days later at the injection energy of 450 GeV per beam.^[9] After the 2009 winter shutdown, the LHC was restarted and the beam was ramped up to half power, 3.5 TeV per beam^[10] (i.e. half its designed energy).^[11] On 30 March 2010, the first planned collisions took place between two 3.5 TeV beams, a new world record for the highest-energy man-made particle collisions.^[12] The LHC will continue to operate at half power for some years; it will not be capable of running at its design power of 7 TeV until 2014.^[13]

Physicists hope that the LHC will help answer many of the most fundamental questions in physics: questions concerning the basic laws governing the interactions and forces among the elementary objects, the deep structure of space and time, especially regarding the intersection of quantum mechanics and general relativity, where current theories and knowledge are unclear or break down altogether. These issues include, at least:^[14]

• Is the theoretical Higgs mechanism for generating elementary particle masses via electroweaksymmetry breaking actually realised in nature?^[15] It is expected that the collider will either demonstrate or rule out the existence of the elusive Higgs boson, thereby either completing or refuting the Standard Model.^[16][17][18]
• Is supersymmetry, an extension of the Standard Model and Poincaré symmetry, realised in nature, implying that all known particles have supersymmetric partners?^[19][20][21]
• Are there extra dimensions,^[22] as predicted by various models based on string theory, and can we detect them?^[23]

• What is the nature of the dark matter that appears to account for 23% of the mass of the universe?

Other questions are:

• 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?
• Why is gravity so many orders of magnitude weaker than the other three fundamental forces? See also Hierarchy problem.
• Are there additional sources of quark flavour mixing, beyond those already predicted within the Standard Model?
• Why are there apparent violations of the symmetry between matter and antimatter? See also CP violation.
• What was the nature of the quark-gluon plasma in the early universe? This will be investigated by heavy ion collisions in ALICE.

  Source

Wikipedia, " Large Hadron Collider", http://en.wikipedia.org/wiki/Large_Hadron_Collider

References