Toward a U.S. role at CERN's new collider.

Tracking the particles created in high-energy, head-on collisions between protons requires massive detectors that can record particle paths to within a millimeter and can precisely measure the energy of these scattered fragments.

Physicists and engineers have teamed up to design and build two such detectors for the Large Hadron Collider (LHC), under construction at the European Laboratory for Particle Physics (CERN) near Geneva (SN: 1/7/95, p. 4). Several hundred U.S. physicists have already formed collaborative groups to participate in this effort.

"Our scientists are heavily involved with their European counterparts in determining the detailed design of both detectors," says John R. O'Fallon, head of the high-energy physics division at the U.S. Department of Energy.

Last week, officials from DOE, the National Science Foundation, and CERN reached agreement on the approximate scale of U.S. involvement in building not only the detectors for the LHC but also the collider itself. The agreement calls for funding from DOE in the range of $400 million to $500 million, divided equally between the collider and detector projects and spread out over 8 to 10 years. The NSF contribution to detector work would be about $80 million over the same period.

Overall, the LHC is expected to cost about $2.7 billion to build, and the cost of its two main detectors would total $1 billion.

The new agreement represents a significant step toward putting U.S. participation in the LHC effort on a firm legal and financial basis. Now, it's up to negotiating teams to work out the technical details of how these funds would be used.

"We think this is positive progress, and we're very pleased to be at this stage of the game," says Martha A. Krebs, director of DOE's energy research office. However, "we are far from finished. There are lots of issues that are going to face us in these negotiations in order to get the best possible arrangement for the U.S."

The LHC is slated to go into CERN's existing tunnel, some 27 kilometers in circumference, which now houses an electron-positron collider. The proposed LHC design requires more than 1,000 high-powered superconducting magnets to accelerate protons to nearly the speed of light and bend their paths to keep them on a steady course around the ring.

When the LHC's two adjacent proton beams, circulating in opposite directions around the ring, are brought together, protons collide at a combined energy of 14 teraelectronvolts. This energy should be high enough for researchers to detect the postulated Higgs boson. Theorists have proposed that this particle is responsible for determining the masses of other fundamental particles, but no one has detected any traces of it at the energies now accessible to particle accelerators.

The builders of both the LHC and its two main detectors face a number of formidable technical challenges. For instance, the collider's magnets must maintain larger magnetic fields than those used previously in accelerators, and they must operate at a frigid 1.9 kelvins, about 300#161#C below room temperature and even colder than liquid helium. Moreover, the LHC's detectors must be able to withstand intense radiation yet rapidly and precisely measure the trajectories and energies of hundreds of millions of photons, electrons, and muons per second.

Officials of DOE hope to reach a final agreement with CERN by November, before preparing the department's 1998 budget for congressional consideration.