Large Hadron Collider

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator, intended to collide opposing particle beams of either protons at an energy of 7 TeV per particle, or lead nuclei at an energy of 574 TeV per nucleus. It is expected that it will address the most fundamental questions of physics, hopefully allowing progress in understanding the deepest laws of nature. The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as much as 175 metres (570 ft) beneath the Franco-Swiss border near Geneva, Switzerland.

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 and of the large family of new particles predicted by supersymmetry. 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.

On September 10, 2008, the proton beams were successfully circulated in the main ring of the LHC for the first time.

Large Hadron Collider "Actually Worked" National Geographic - September 10, 2008

Scientific wonder comes to life MSNBC - September 10, 2008

On September 19, 2008, the operations were halted due to a serious fault between two superconducting bending magnets. Repairing the resulting damage and installing additional safety features took over a year.

LHC gets colder than deep space BBC - October 16, 2009

On November 20, 2009 the proton beams were successfully circulated again.

On November 23, 2009, the first protonproton collisions were recorded, at the injection energy of 450 GeV per particle.

Large Hadron Collider sets world energy record BBC - November 30, 2009

On December 18, 2009 the LHC was shut down after its initial commissioning run, which achieved proton collision energies of 2.36 TeV, with multiple bunches of protons circulating for several hours and data from over one million proton-proton collisions.

Large Hadron Collider produces first physics results

Collider Meets Its Goal for Power New York Times - December 9, 2009

February 2010: LHC resumed operations at half of the design collision energy

First results from Large Hadron Collider published

First physics from the Large Hadron Collider's CMS detector PhysOrg - February 17, 2010

In 2012 it will be shut down for the repairs necessary to bring it to its full design energy, and then it will start up again in 2013.

Purpose

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 about two to three years to collect enough data to discover the Higgs boson unambiguously. Similarly, it may take one year or more before sufficient results concerning supersymmetric particles have been gathered to draw meaningful conclusions.

Physicists hope that the LHC will help answer 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:

Is the Higgs mechanism for generating elementary particle masses via electroweak symmetry breaking indeed realised in nature? It is anticipated that the collider will either demonstrate (or rule out) the existence of the elusive Higgs boson(s), completing (or refuting) the Standard Model.
Is supersymmetry, an extension of the Standard Model and Poincare symmetry, realized in nature, implying that all known particles have supersymmetric partners?These may clear up the mystery of dark matter.
Are there extra dimensions, as predicted by various models inspired by string theory, and can we detect them?

Design

The LHC is the world's largest and highest-energy particle accelerator. 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 (160 to 570 ft) underground.

The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the Large Electron-Positron Collider. 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.

The LHC physics program is mainly based on protonproton 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 ion.

The lead ions will be first accelerated by the linear accelerator LINAC 3, and the Low-Energy Ion 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 (or 575 TeV per ion), higher than the energies reached by the Relativistic Heavy Ion Collider. The aim of the heavy-ion program is to investigate quarkgluon plasma, which existed in the early universe.

Detectors

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.[21] 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.

List of Large Hadron Collider experiments

Micro black holes

Although the Standard Model of particle physics predicts that LHC energies are far too low to create black holes, some extensions of the Standard Model posit the existence of extra spatial dimensions, in which it would be possible to create micro black holes at the LHC at a rate on the order of one per second. According to the standard calculations these are harmless because they would quickly decay by Hawking radiation. The concern is that among other disputed factors, Hawking radiation (the existence of which is still debated) is not yet an experimentally-tested or naturally observed phenomenon.