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Speaker Sees New Collider as a Cooperative Effort to Solve Nature's Mysteries
Photograph by Harvey Leifert
The Large Hadron Collider, the world's newest and largest particle accelerator, is poised to expand knowledge of the unseen 96% of the universe. When fully operational in 2009, the collider will focus on several primary missions: the search for the elusive—and unproven—Higgs boson particle, along with dark matter and dark energy.
But even before any new discoveries, the collider has proven to be a model of international science cooperation, Lyndon Evans, project director for the collider, said at a Capitol Hill briefing organized by AAAS. Better known as LHC, the collider is based in Switzerland and straddles the French-Swiss border. In addition to 20 European member states, participating countries include Canada, Japan, India, Israel, Russia, and the United States, and all have contributed funds and scientific expertise.
Similarly, scientists will be able to conduct experiments using the LHC without ever visiting Switzerland, he said. LHC will produce a massive stream of data—10 to 15 million gigabytes per year, in Evans's estimation. Long before the Worldwide Web became a ubiquitous tool, the collider's designers had decided that scientists would use the Web to access that information. The Web will provide scientists "seamless access to data," channeled through scientific institutions in participating countries, Evans said. In the United States, Fermilab in Illinois and Brookhaven National Laboratory in New York will play that role.
Evans spoke in Washington, D.C., at a 14 November briefing organized by the AAAS Center for Science, Technology, and Security Policy. The talk also was sponsored by the American Physical Society, and the British Embassy.
This computer-generated image shows the location of the 27-km LHC tunnel (in blue) on the Swiss-France border. The four main experiments (ALICE, ATLAS, CMS, and LHCb) are located in underground caverns connected to the surface by 50 m to 150 m pits. Part of the pre-acceleration chain is shown in grey.
Image and caption © CERN
LHC is located at the European Organization for Nuclear Research (better known as CERN), in Geneva, Switzerland. Founded in 1954, in the aftermath of World War II, CERN was established in Geneva "because it was neutral, and it was cheap," Evans said. "It is still neutral," he added, to laughter from the 120 attendees.
The Large Hadron Collider has operated only briefly, and today is undergoing a complex set of repairs. But the particles will zip around the 17.1-mile (26.7-kilometer) collider ring at just shy of the speed of light--11,000 times per second.
Particle accelerators are time machines, Evans explained. They help us to see back in time to within nanoseconds of the Big Bang, when the submicroscopic components of the universe were created. Collisions between particles can produce mass, as occurred back then. Discoveries at the collider could complement the discoveries of the Hubble Space Telescope, which searches for large objects at the farthest edges of the universe, formed as much as a billion years ago.
Scientists employ a Standard Model to describe particle physics. Basically, as Evans put it, the model says that matter is composed of fermions (six quarks and six leptons); all particles have antiparticles; and forces (strong, weak, and electromagnetic) are transmitted by the exchange of bosons. But, the Standard Model leaves some key questions unanswered, and even unaddressed, he said. Why, for example, do particles have mass? Does the posited Higgs boson actually exist? Why are matter and antimatter not symmetrical? What are dark matter and dark energy?
Thus far, physicists can only infer the existence of dark matter and dark energy. Dark energy is thought to affect the rate of expansion of the universe, constituting around 73 percent of it. Dark matter, around 23 percent of the universe, is suggested by the effect of gravity on the visible matter, which constitutes just four percent of the universe. The Higgs boson is the only particle predicted by the Standard Model that has yet to be found. Physicists describe its role—if it exists—as that of providing mass to other particles.
LHC was designed to take on these fundamental and difficult questions, Evans said. It follows a line of increasingly sophisticated accelerators, starting with the one built by Ernest O. Lawrence and M. Stanley Livingston in Berkeley, California, in 1930; it had a diameter of just five inches (around 13 centimeters) and could easily be held in the palm of one's hand.
Today's large accelerators benefit more from new technologies than from greater funding, according to Evans. The CERN budget has remained essentially flat for decades, in constant Swiss francs, he said. Superconductivity, the use of which use began in the 1980s, permits modern accelerators—large though they are—to be much smaller than if they had to rely on classical electromagnets to speed particles on their way. Superconductivity describes a property of mercury manifested when it is cooled to 4.2 Kelvin (-450° Fahrenheit), close to the coldest temperature possible. It was discovered in 1911, three years after helium was first liquefied, permitting such low temperatures to be attained.
Evans noted that LHC consumes 40 megawatts of power to cool liquid helium to nearly 0 Kelvin, which allows superconductivity to function within its 23 kilometers (14 miles) of specially designed magnets. Although LHC is the world's largest accelerator, an equivalent facility using traditional electromagnets would require a circumference of 100 kilometers (62 miles) and would consume 100 megawatts of power, he said.
LHC requires not only extremely low temperature to function, said Evans, but also a virtually absolute vacuum. Particles will cover many times the distance from Earth to Sun over dozens of hours, and during that journey, they must not encounter a molecule of air more often than once every 500 million kilometers (300 million miles).
The first test of the completed LHC took place on 10 September, but just nine days later it was shut down due to an electrical fault. One faulty splice—out of 10,000—resulted in an arc that produced a large helium leak, Evans said. Some 20 magnets must be replaced, a process that will take months. He said that the repairs will be a slow process: First, it takes two months to raise the temperature of the supercooled helium to room temperature, and after repairs are made, it will take another two months to cool the helium back down to its operating temperature. LHC will not be operational before May 2009, according to news reports.
Evans was asked whether there will be a "Eureka!" moment if the Higgs boson is discovered. The answer: Apparently not. Rather, he said, the discovery will likely be based on the analysis of a huge accumulation of data over a long period of time. "This is the most sophisticated scientific project ever built," he said, and it should be operating for 20 years or more. He cautioned his audience not to anticipate quick results, but added that within five years, we should have a good indication of what may be coming.
The Higgs boson may be easy or difficult to find, Evans added. And, in addition to resolving questions about asymmetry, dark matter, and dark energy, LHC will likely answer other questions that have yet to be posed.
Most of the components of the Large Hadron Collider were constructed in the 27.6 kilometer ring deep underground. One major unit, the Compact Muon Solenoid (CMS) was, however, built on the surface, then lowered in sections down a shaft to be reassembled below. This required excavating an area, known as Site 5, in Cessy, France.
"When we started preparing the work site for CMS," says project leader Lyndon Evans, "we found something that nobody ever wants to find when you're doing a big engineering project: an archeological site."
"We found the remains of a Roman villa" dated to the 4th century A.D., Evans said, and that delayed work on the CMS while archeologists studied the find. One important discovery, he said, was that the sides of the villa align perfectly with those of present-day property lines in Cessy, and these are not simple north-south, east-west lines as would be typical in the United States. This means, he said, that the current land registry in Cessy dates back to the Roman occupation.
The site also yielded coins dating to 310 and 315 A.D, minted near Rome. These, not the euro, were the first common European currency, Evans noted to laughter.
3 December 2008