Lincoln (Neb.) - Dec. 8, 1997 - University of Nebraska physicists will play an important role in a U.S.-European effort to research the basic structure of matter.
In an agreement signed Dec. 8 by U.S and European officials in Washington, D.C., the United States will invest $531 million over the next eight years in a new particle accelerator, the Large Hadron Collider, under construction near Geneva, Switzerland.
When completed in 2005, the accelerator - with a circumference of 16 miles - will be the world's most powerful. The LHC is being built at the European Laboratory for Particle Physics, known as CERN, and will bring protons into head-on collision at higher energies than ever achieved before to allow scientists to penetrate still further into the structure of matter.
The Nebraska team, headed by associate professor Greg Snow and assistant professor Dan Claes, will eventually number about eight, including physicists, technicians and graduate students. It will be responsible for what Snow called a "small but important" part of one of the two major experiments scheduled for the new collider, the CMS (Compact Muon Solenoid) experiment.
"We are responsible for providing the equipment for the measurement of what is called the 'luminosity' of the experiment, which is a measure of the intensity of the colliding particle beams at the very interaction region where our experiment will sit," Snow said.
The instrument the Nebraska team will build in Lincoln and transport to Geneva in about 2003 will consist of plastic panels of a material called "scintillator," so named because when a charged particle goes through it, light is generated in the plastic. The panels will be connected to devices that are sensitive to that light and will allow the scientists to count particles that emerge from the collision region. There also will be detectors located some distance from the interaction region, but placed as close as 1 centimeter from the particle beam, enabling the scientists to count particles that emerge at very low angles. This should allow them to count particles that emerge from the collision region for any type of interaction that happens.
"Most collisions are of a grazing nature and particles barely emerge from the beam," Claes said.
"The most interesting physics, where particles are created, is usually associated with activity that flies out away from the beam pipe. Those events are rare, but we need to be able to establish how rare they are by counting how often that we see the physics that we're interested in, compared to how often there is a real collision."
Snow said the LHC will produce many times the number of top quarks than were produced at Fermilab outside of Chicago, where he was involved in the first verified observance of the top quark in 1995. One item on the LHC's long menu is a detailed study of the production and decay properties of the top quark, the last basic particle of matter to be found. Another is the search for the Higgs boson, the last missing piece in what is called the Standard Model of particle physics.
"In the theoretical framework of the Standard Model, the Higgs boson is the particle which explains how all other particles, including quarks, get mass," Snow explained. "If we find it, our picture of high-energy physics and particle interaction, the Standard Model, is complete and true. Without it, we'll have to find some other way to explain everything."
The LHC has an estimated total cost of nearly $6 billion and is being built inside an existing accelerator tunnel on the French-Swiss border. In the collider, radio frequency energy will accelerate beams of protons to nearly the speed of light. Powerful superconducting magnets will guide the counter-rotating beams to collision points around the accelerator. The collision energy of 14 trillion electron volts will be seven times greater than the world's present highest energy accelerator, the Tevatron at Fermilab. The collisions will occur at the rate of 1 billion per second.
Snow said the agreement ends a long period of uncertainty for the U.S. high-energy physics community since Congress stopped funding for the Superconducting Super Collider in Waxahatchie, Texas, in 1993. That facility would have been the world's largest particle accelerator.
"We're very excited about this. It sort of cements the activities of U.S. physicists who have been working on these LHC experiments the last three or four years," he said.
"Not long after the Superconductor crashed in the autumn of 1993, which was right after I came to Nebraska to start a group that would be working at that facility, a large number of U.S. physicists joined the big experiments that are planned for the LHC. This agreement is the end of an era where the U.S. high- energy physics community didn't know what its future was."
Working at CERN will be a homecoming for Snow as he did his
postdoctoral research there. Besides, he said, Switzerland has
another advantage over Texas: "You can't compare the skiing."
EDITORS' NOTE: More information on the Large Hadron Collider and
photographs that can be downloaded are available on the World
Wide Web at http://www.cern.ch.
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