Where Large Hadrons Collide
Talks among representatives of the Department of Energy, the National Science Foundation, and CERN management began in 1995, soon after the LHC was formally approved by the CERN Council. Under terms approved by Congress and signed in December 1997 by Energy Secretary Federico Peņa, National Science Foundation Director Neal Lane, CERN Council President Luciano Maiani, and CERN Director General Christopher Llewellyn Smith, the U.S. will invest $531 million in the accelerator and its two main detectors. About 85 percent of those funds will come from DOE and the remainder from NSF.
Others among the half dozen nonmembers who eventually signed on to help build the accelerator itself were Japan, Russia, and Canada. While the U.S. investment amounts to only ten percent of the LHC's cost including detectors, Americans will make up 20 percent of its users.
Berkeley Lab is a major player among the six national laboratories and five dozen American universities involved in the LHC. Through the Accelerator and Fusion Research Division, under the leadership of William Turner, the Lab is designing superconducting cable for the magnets in the main ring and will design and build cryogenics and quadrupole focusing magnets. And under the leadership of Gil Gilchriese of the Physics Division, the Lab is playing a crucial role in building the ATLAS detector.
"We can study only a small fraction of these events, so we have to sift the possibilities like a miner panning for gold," says Gil Gilchriese, who heads the Berkeley Lab group working on the ATLAS Inner Detector. "We establish electronic filters so that nearly one billion collisions every second are quickly culled to 100,000 of interestthe rest are dumped. A more sophisticated filter reduces that 100,000 to a few thousand, and finally a 'farm' of hundreds of computers picks a hundred or so of those to record on tape, so they can be studied later."
To capture the raw events, ATLAS uses concentric layers of detectorslayers inside layerswrapped around the beam line. Outermost are the muon detectors and the hadron and electromagnetic calorimeters, which record particle energies. For the muon detectors, toroidal air-core superconducting magnets create a strong magnetic field which bends the paths of charged particles according to their signs and momenta; the magnetic field for the Inner Detector is provided by a superconducting solenoid.