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Great Chance to View World's Largest Particle Accelerator, the Large Hadron Collider On 6 April 2008
:: 19 March, 2008
On 6 April 2008, CERN will open its doors to the public, offering a unique chance to visit its newest and largest particle accelerator, the Large Hadron Collider (LHC), before it goes into operation later this year. This scientific instrument, the largest and most complex in the world, is installed in a 27km tunnel, 100 metres underground in the Swiss canton of Geneva and neighbouring France. CERN will open all access points around the ring for visits underground, to the tunnel and the experiment caverns. On the surface, a wide-ranging programme will be on offer, allowing people to learn about the physics for which this huge instrument is being installed, the technology underlying it, and applications in other fields.
In the LHC, particles such as protons or heavy ions will be accelerated to close to the speed of light in two tubes. At four intersection points the particles will collide at an energy never before reached in a particle accelerator to study new areas of physics that so far have not been accessible. Experiments at the LHC expect to be able to answer a number of fundamental questions, such as the origin of mass or the nature of the so-called “dark matter”. However, since the LHC will explore a new energy range, there will also be unexpected results, resulting in new questions and new physics.
On the Open Day, many visitors to CERN will be able to descend and see the LHC and its big experiments, ALICE, ATLAS, CMS and LHCb in place in their underground caverns. However, since access to the underground areas is limited due to the capacity of the elevators and safety concerns, a range of activities is also planned on the surface where visitors will be able to learn about particle physics and talk to CERN engineers and physicists.
A central theme apart from the LHC, its magnets and experiments, will be superconductivity, the principle on which the operation of the LHC is based. At the heart of the LHC magnets lie 7000 kilometres of superconducting cables, cooled to a temperature close to absolute zero, which are able to conduct electricity without resistance. Spectacular experiments, exhibitions and films will introduce the public to this exciting phenomenon, visitors will be able to meet physicists to “ask an expert” and there will be the chance for an encounter with two Nobel laureates who will give lectures about their prize-winning discoveries.
The fun and excitement of physics will be demonstrated in the Globe of Science and Innovation and physics shows taking place at various venues around the ring. Children will be able to meet up with the presenter of a popular French TV show on his tour through eight communes close to the LHC access points or take part in a “magical physics” show.
Note for Large Hadron Collider
The Large Hadron Collider (LHC) is a particle accelerator and hadron collider located at CERN, near Geneva, Switzerland (46°14′N, 6°03′E). Currently under construction, the LHC is scheduled to begin operation in May 2008. The LHC is expected to become the world's largest and highest-energy particle accelerator. The LHC is being funded and built in collaboration with over two thousand physicists from thirty-four countries as well as hundreds of universities and laboratories. When activated, it is theorized that the collider will produce the elusive Higgs boson, the observation of which could confirm the predictions and 'missing links' in the Standard Model of physics and could explain how other elementary particles acquire properties such as mass. 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 fundamental forces: electromagnetism, the strong force, and the weak force. The Higgs boson may also help to explain why the remaining force, gravitation, is so weak compared to the other three forces. In addition to the Higgs boson, other theorized novel particles that might be produced, and for which searches are planned, include strangelets, micro black holes, magnetic monopoles and supersymmetric particles.
The collider is contained in a circular tunnel with a circumference of 26.659 kilometres (16.5 miles), at a depth ranging from 50 to 175 metres underground. The tunnel, constructed between 1983 and 1988, was formerly used to house the LEP, an electron-positron collider.
The 3.8 metre diameter, concrete-lined tunnel actually crosses the border between Switzerland and France at four points, although the majority of its length is inside France. The collider itself is located underground, with many surface buildings holding ancillary equipment such as compressors, ventilation equipment, control electronics and refrigeration plants.
The collider tunnel contains two pipes enclosed within superconducting magnets cooled by liquid helium, each pipe containing a proton beam. The two beams travel in opposite directions around the ring. Additional magnets are used to direct the beams to four intersection points where interactions between them will take place. In total, over 1600 superconducting magnets are installed, with most weighing over 27 tonnes.
The construction of LHC was originally approved in 1995 with a budget of 2.6 billion Swiss francs, with another 210 million francs (140 M€) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (300 M€) in the accelerator, and 50 million francs (30 M€) for the experiments, along with a reduction in CERN's budget pushed the completion date out from 2005 to April 2007. 180 million francs (120 M€) of the cost increase has been the superconducting magnets. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid. The total cost of the project is anticipated to be between $5 and $10 billion.
Note for Dark Matter
In astrophysics and cosmology, dark matter is a hypothetical form of matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures larger than galaxies, as well as Big Bang cosmology, dark matter accounts for the vast majority of mass in the observable universe. The observed phenomena consistent with dark matter observations include the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter also plays a central role in structure formation and galaxy evolution, and has measurable effects on the anisotropy of the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation: the remainder is called the "dark matter component".
The composition of dark matter is unknown, but may include ordinary and heavy neutrinos, recently postulated elementary particles such as WIMPs and axions, astronomical bodies such as dwarf stars and planets (collectively called MACHOs), primordial black holes and clouds of nonluminous gas. Also, matter which might exist in another universe but might affect ours via gravity would be consistent with some theories of brane cosmology. Current evidence favors models in which the primary component of dark matter is new elementary particles, collectively called non-baryonic dark matter.
The dark matter component has vastly more mass than the "visible" component of the universe. At present, the density of ordinary baryons and radiation in the universe is estimated to be equivalent to about one hydrogen atom per cubic metre of space. Only about 4% of the total energy density in the universe (as inferred from gravitational effects) can be seen directly. About 22% is thought to be composed of dark matter. The remaining 74% is thought to consist of dark energy, an even stranger component, distributed diffusely in space. Some hard-to-detect baryonic matter makes a contribution to dark matter, but constitutes only a small portion. Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics. It has been noted that the names "dark matter" and "dark energy" serve mainly as expressions of human ignorance, much as the marking of early maps with "terra incognita".
Much of the evidence for dark matter comes from the study of the motions of galaxies. Many of these appear to be fairly uniform, so by the virial theorem the total kinetic energy should be half the total gravitational binding energy of the galaxies. Experimentally, however, the total kinetic energy is found to be much greater: in particular, assuming the gravitational mass is due to only the visible matter of the galaxy, stars far from the center of galaxies have much higher velocities than predicted by the virial theorem. Galactic rotation curves, which illustrate the velocity of rotation versus the distance from the galactic center, cannot be explained by only the visible matter. Assuming that the visible material makes up only a small part of the cluster is the most straightforward way of accounting for this. Galaxies show signs of being composed largely of a roughly spherically symmetric, centrally concentrated halo of dark matter with the visible matter concentrated in a disc at the center. Low surface brightness dwarf galaxies are important sources of information for studying dark matter, as they have an uncommonly low ratio of visible matter to dark matter, and have few bright stars at the center which impair observations of the rotation curve of outlying stars.
According to results published in August 2006, dark matter has been observed separate from ordinary matter through measurements of the Bullet Cluster, actually two nearby clusters of galaxies that collided about 150 million years ago. Researchers analyzed the effects of gravitational lensing to determine total mass distribution in the pair and compared that to X-ray maps of hot gases, thought to constitute the large majority of ordinary matter in the clusters. The hot gases interacted during the collision and remain closer to the center. The individual galaxies and the dark matter did not interact and are farther from the center.
Tags: CERN , particle accelerator , Large Hadron Collider (LHC) , dark matter , ALICE , ATLAS , CMS , LHCb , ,
