U.S., Berkeley Lab To Take Part in International Collaboration on Large Hadron Collider

December 19, 1997

By Paul Preuss, paul_preuss@lbl.gov

On Monday, Dec. 8, U.S. Secretary of Energy Federico Peña, National Science Foundation Director Neal F. Lane, and CERN Council President Luciano Maiani signed a precedent-setting agreement between the United States government and CERN, the European Laboratory for Particle Physics.

Over the next eight years the Department of Energy will invest $450 million and the National Science Foundation $81 million in constructing the Large Hadron Collider (LHC) and two of its giant particle detectors near Geneva, Switzerland -- the first time the US will contribute significantly to the construction of an accelerator outside this country. Japan, Canada, and Russia are among several other contributors who are not member nations of CERN.

When it begins operating in 2005, the LHC will be the world's most powerful proton-proton collider, achieving energies of 14 TeV (trillion electron volts) at the point where the two counter-rotating beams of protons meet head on.

"As Congress required, US involvement is concentrated in the interaction regions," says William Barletta, director of Berkeley Lab's Accelerator and Fusion Research Division (AFRD). "Brookhaven is building the dipole magnets, and along with Fermilab, AFRD is designing the quadrupole focusing magnets for one of the experiments."

The pixel detector system
The Lab's Physics Division is working on the pixel detector system, the innermost detector in the ATLAS experiment to be built for the Large Hadron Collider
AFRD will also provide the cryogenics for magnets built by Berkeley Lab and others.(Super-conducting magnets must be cooled to the temperature of liquid helium.) William Turner is the Lab's LHC project leader.

The polyamide-insulated, copper-jacketed, niobium-titanium superconducting cable to be used by all the magnets in the LHC ring was designed by AFRD and will be tested at Brookhaven. US and European firms will manufacture the final product.

"We're also building beam collimators and neutral dumps to keep particle debris from ruining the magnets," says Barletta. "Once the collimators are installed they can be used as a first-order monitor of beam luminosity, before the detectors are finished."

The principal quarry of all this energy and luminosity is the Higgs boson (or family of bosons), the carrier of the Higgs field, which is thought to impart mass to all particles with mass, including the predicted massive "sparticles" of supersymmetry theory. The Higgs boson is weakly interacting, and will be seen only rarely in the debris of millions of proton collisions.

The five-story high, 7,000 ton ATLAS experiment is designed primarily to find the Higgs. "We're working on the pixel detectors and the silicon strips," explains Physics Division director James Siegrist referring to the experiment's innermost components. "Murdock Gilchriese is the ATLAS group head for silicon systems," he says; "With collaborators from Japan and UC Santa Cruz, we led the development of this kind of detector for the Superconducting Super Collider. We're carrying over a lot of design ideas from the SSC and building on what we learned."

The silicon strips will be similar to those built for the CDF experiment at Fermilab, which was instrumental in snaring the top quark. "In ATLAS they'll get hit at a much higher rate, once every 25 nanoseconds," says Siegrist, "and there are more of them, adding up to some 60 square meters of silicon."

"Radiation will be an order of magnitude higher than it would have been even in the SSC," says Siegrist, "so we also have to make the detectors rad hard."

Close to the beam line, overlapping layers of tiny pixel elements will be used to reduce the area of individual units subject to radiation hits. The electronics will be "bump-bonded" with silicon to form chips incorporating 15,000 transistors each -- about 900,000 transistors in all, feeding 250 million channels of data. "We have to get data out of each pixel. We have to get heat out. We have to get power in," says Siegrist. "A simple idea -- but in practice, anything but simple."

About a fifth of the scientists working to build the experiments will be from the US, most of them from Fermilab, Brookhaven, and Berkeley Lab, as well as three other DOE laboratories and 60 universities. When the LHC achieves first light in 2005, the US will have supplied about 10 percent of the total cost of the accelerator and experiments -- 85% of this sum coming from the Department of Energy -- although US researchers will make up 20 percent of those using the detectors. A quarter of the high-energy physics experimenters in the US plan to work at CERN.

Upon signing the precedent-setting CERN-USA pact, Energy Secretary Peña said, "I have no doubt that when the history of the next 50 years is written, the Large Hadron Collider and all of the science, new ideas, and technologies it spawns will be a major chapter."

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