| VOL. 23, NO. 13||JANUARY 30, 1998 |
Columbia Team of Scientists Will Help Build the Worlds Most Powerful Accelerator
BY BOB NELSON
olumbia physicists will receive $13 million to provide the most sensitive electronics ever made to detect bursts of new particles within the Large Hadron Collider, the European accelerator that may reveal why matter has mass.
Under an agreement signed by American and European negotiators last month in Washington, the United States will contribute $531 million over the projects 9-year construction period.
The electronics, one of several University collaborations to build the collider, are to be built by a Columbia team directed by John Parsons, associate professor of physics. They will measure the energies of dozens of particles created when two protons moving at a speed close to that of light collide within the ATLAS particle detector, one of four at the collider. Physicists expect there will be about 40 million such collisions each second in the space of five centimeters, or about two inches, meaning the electronics will have to be among the most sensitive ever made.
With a circumference of almost 17 miles that crosses under the French-Swiss border outside Geneva, the Large Hadron Collider, when completed in 2005 at a cost of nearly $6 billion, will be the worlds most powerful particle accelerator. It is being built at the European Laboratory for Particle Physics, known as CERN.
William J. Willis, the Higgins Professor of Physics at Columbia and American spokesman for the ATLAS experiment, will manage $165 million of the American contribution to the ATLAS detector. The funding goes to national laboratory and university subcontractors providing various pieces of equipment.
The project was almost derailed early last year when some members of Congress expressed concern about U.S. fiscal exposure to the international project. Willis and Ellen S. Smith, assistant vice president and director of federal relations at Columbia, organized a group of scientists and government relations staff to educate key members of Congress, an effort that helped return the LHC to the Congressional agenda.
The Large Hadron Colliders two general purpose particle detectors, each five stories high, weighing thousands of tons and costing nearly $1 billion apiece, will record the shower of subatomic particles from the collisions. Two smaller detectors will serve more specialized purposes. Columbias research team, including research scientists Michal Seman and Misha Leltchouck, played a central role in the design of a key element of the ATLAS detector, called an electromagnetic calorimeter, which captures these particles and measures their energy. Using these results, scientists can attempt to reconstruct what took place in the high-energy collisions, and can search for signatures of new particles or other unexpected phenomena.
|The ATLAS experiment, one of two house-sized particle detectors being constructed underground at the Large Hadron Collider in Geneva. Protons accelerated at speeds close to that of light will enter the detector from opposite directions and collide at the inner detector. Electromagnetic calorimeters (EM calorimeters) designed at Columbia will capture particles thrown off in collisions and measure their energy, as will other calorimeters and detectors.|
The calorimeter, which is of a general type first proposed by Willis and colleagues more than 20 years ago, uses electrified lead plates and liquid argon, a dense, nonreactive substance, to detect particles created in collisions. It is to be constructed at three sites in France.
The electronic system that detects collisions for ATLAS pushes the state of the art, Parsons said. It is spread across a barrel-shaped space about seven meters long inside the detector and will be divided into some 200,000 tiny squares, each of which can detect a particle and measure its energy, so that the direction of the ejected particles can be determined as well as their energy. The electronics were designed, and are to be constructed, by Parsons and research scientists Nicolo Cartiglia and Al Gara, along with Columbias Nevis Laboratories engineering staff. The system should be ready for final production by 2000, Parsons said. The Columbia group, including Parsons and research scientist Jeremy Dodd, will be among the foremost analysts of the results once operations begin in 2005.
The new collider will help scientists answer questions such as: Why does matter have mass? Why is the universe made mostly of matter, not antimatter? Are there still more fundamental particles yet unknown to physics? Do these particles make up the universes dark matter, the mysterious substance that makes up 90 percent of the universe but has never been seen?
The current theory, known as the Standard Model, postulates that particles acquire mass, defined as resistance to acceleration, through their interaction with a so-called Higgs field that permeates all space. According to this theory, an as yet undiscovered particle, the Higgs boson, would have to exist. The LHC should prove once and for all whether it actually does exist.
Many physicists are skeptical, Parsons said. From the theory and from previous experiments, we know that the Higgs boson, if it exists, must have a mass within a certain range. However, there are theoretical reasons suggesting a mass in this range would not be very natural. One popular solution is supersymmetry, in which every particle has a cognate called a superparticle. No such supersymmetrical particles have ever been observed, but the LHC could well find some, Parsons said.