When the U.S.-led Superconducting Super Collider project was canceled in 1994, the U.S. particle physics community was in disarray. Scientists who probe the structure of matter believed that the SSC, because of its potential tremendous power, was the only tool that could unravel some of nature's most profound questions -- perhaps definitively.

Although some years off, a new project has galvanized researchers, including a team of Penn physicists, with the promise of a machine that could give them the clearest glimpse yet of the fundamental forces that shape the universe.

The Large Hadron Collider (LHC), the next generation of particle accelerators, is set to begin operation in 2005 at the European Laboratory for Particle Research known as CERN. LHC is a $5 billion scientific facility built in collaboration with 19 European nations and other nations throughout the world. It will have seven times the power of the world's largest accelerator and will produce 10 times the number of particle collisions (called luminosity).

The LHC is being hailed as the new frontier in physics. It will allow scientists to "see" the results of collisions of protons at previously unattained energies. From the scattered debris of these collisions, scientists will be able to piece together a clearer understanding about how the physical world works.

According to Penn physicist Brig Williams, LHC will offer an historic chance to test theories about how the universe, which in its earliest seconds existed only as energy, came to have the solid form we call mass. Planned experiments may also prove whether the Standard Model -- the most successful of current theories that explain the physical forces that govern the universe -- is correct.

Williams and the Penn team will be among the leaders spearheading the U.S. involvement in LHC. Although the U.S. is not a member of the LHC coalition, it will contribute to the costs of construction and research, in part to make up for the lack of any U.S. facility capable of the power anticipated for LHC.

The U.S. is expected to contribute more than $150 million toward the LHC project and experiments. Funding will come from the Department of Energy and the National Science Foundation.

At the heart of the U.S. effort will be two experiments: Atlas and the Compact Muon Solenoid (CMS). Both Atlas and CMS are detectors utilizing magnets that will help researchers track the events occurring at the high energies generated by the LHC.

Atlas will fill a five-story building and utilize torridal or ring-shaped magnets to measure sub-atomic particles "created" in the collisions. Many of these particles exist for tiny fractions of a second, thus challenging scientists to develop new ways to track and identify the unique signatures of the collision debris.

When Atlas begins producing data, it will be an important moment for the team of Penn researchers who have been responsible for designing much of the sophisticated electronics the device will use to gather data. Williams, who leads Penn's high-energy physics group, said that Atlas represents input from scientists from more than 100 universities and laboratories, including 26 universities and four national labs from the United States.

"This is the plus of 'big science.' We will be able to tap the tremendous intellectual resources of many U.S. institutions and other institutions around the world in making a contribution to the LHC experiment," he said.

Williams noted that U.S. institutions represent about 20 percent of the overall LHC scientific corps. Many of the U.S. researchers were involved in developing experiments for the SSC project, and will bring the results of decades-long effort and expertise originally targeted for the canceled U.S. project.

Williams has been heavily involved in the LHC project for many years. He is one of two U.S. members of the Atlas executive board, responsible for the overall management of the multi-nation project. As coordinator of high-speed electronics devices, he's in charge of the parts of the machine that make sense of the results of the collisions. He travels to CERN nine or ten times a year and has been a leading proponent of the importance of the project to U.S. leadership in the particle physics field.

Penn's high energy physics group has garnered a national reputation as one of the top teams in its field. The group played a prominent role in the 1995 discovery of the top quark, an elusive subatomic particle that was the last undiscovered quark of the six expected in the Standard Model. The group also has made important innovations in the design of computer chips used in high speed detectors. Penn designs will be used in five large international experiments in the United States and elsewhere, and more than 15 other high energy physics groups throughout the world have shown interest in using the circuits. Penn receives about $3.5 million in federal research support each year for a combination of theoretical and experimental projects.

High energy physics has been compared to trying to figure out how a pocket watch works by smashing two watches together and then tracing the path of the tiny gears and other small parts as they leave the collision, to make guesses about their function. This is roughly the task of the particle physicist attempting to probe the structure of matter by smashing protons together.

The scientists are hoping the LHC may give them a chance to observe the Higgs particle. Confirmation of the Higgs particle would fill in one of the more elusive pieces of the puzzle missing from the Standard Model. Higgs is believed to play a role in explaining why matter has mass.

According to theory, there exists a Higgs field, which can be understood as the "ether" pervading the universe. There is a statistical probability that a Higgs particle will exist at any point in space. The Higgs particle interacts with elementary particles and "imparts" mass to them. It does not interact with photons or other massless components of matter.

The LHC's high energies may give scientists a chance to observe the Higgs particle, and that would be the biggest prize yet.

Return to Compass Features for September 17, 1996