Edition: U.S. / Global

Swiss Physicists Face Decision In Race for Atomic Particle

Published: September 6, 2000

Suspicions that they are seeing sketchy evidence for a long-sought particle has put physicists in Geneva in a quandary over whether to proceed with building a $4 billion particle accelerator or to continue experiments with the current equipment.

Like their rivals at the Fermi National Accelerator Laboratory outside Chicago, the Geneva physicists, at the laboratory known as CERN, for its French acronym, have been searching for a particle called the Higgs boson, which theoretical physicists believe may be the source of all mass in the universe -- in effect, the reason matter has weight.

But the accelerator in Geneva that is producing the data is scheduled to be shut on Oct. 1, so that the new machine can be constructed in the same underground tunnel. The new machine, which is to have a $500,000 contribution from the United States, would almost certainly be powerful enough to see the Higgs, assuming that it exists, by 2005 or 2006.

The trouble for the Geneva scientists is that an upgraded machine at Fermi may be powerful enough to make the discovery first, after beginning operation next spring. CERN physicists, who generally favor an extension for their existing equipment, met yesterday to present data from their particle detectors.

''Of course, we are all thrilled,'' said Dr. Tiziano Camporesi, spokesman for the group that is working on one of the four large particle detectors at the accelerator. ''We have been on this machine for more than 10 years now, and clearly this is the first time we have seen something which might give a hint of a discovery'' of the Higgs.

Next week, an advisory panel at CERN will make a recommendation to the director general of the lab, Prof. Luciano Maiani, on continuing the experiments for up to several months longer. Dr. Roger Cashmore, the research director of the accelerator and a member of the panel, said that despite the physicists' enthusiasm it was still not clear what the recommendation would be.

''We have to balance whether we can turn an excitement into a bona fide reliable physics signal against big delays to the next big project inside CERN,'' Dr. Cashmore said.

For decades, particle physicists have worked out a complex theory, the Standard Model, which accounts for the masses of all the known particles. It also seems to explain three of the four known forces by which particles in the universe interact, or exert forces, on one another.

Those three are the strong nuclear force, which holds together atomic nuclei; the weak nuclear force, which causes radioactive decay; and the electromagnetic force, whose effects are familiar from magnets and electrically charged rods but which also operates at the subatomic level. The force of gravity, described by Einstein's theory of relativity, has not been successfully incorporated into the Standard Model.

For the model to predict the particle masses, it requires the existence of one particle unlike any other -- the Higgs boson. By filling space with a molasseslike field of energy, the Higgs serves as a sort of wellspring of mass for other particles. But when those particles are smashed together violently enough in particle accelerators, the Higgs should appear as a particle itself.

The precise mass of the Higgs is uncertain. The heavier it is, the more powerful the accelerator that will be required to create it in those collisions. Most of the excitement at CERN has flowed from signals indicating that three Higgs bosons may have been captured in one of the big particle detectors at an energy of 115 billion electron volts. The mass of a hydrogen atom, expressed in those units, is 1 billion electron volts. But the signals could simply be statistical flukes, and more data could confirm the signal or wipe it out.

If the Higgs is too heavy to be seen by the existing accelerator, called LEP, the Fermi lab's upgraded machine will have a shot at it. ''Globally, everybody would like the Higgs boson to be found tomorrow,'' said Dr. Chris Quigg, a Fermilab theorist. ''On the other hand, some of my colleagues can't quite keep themselves from hoping that it's really there, but LEP can't quite confirm it.''

If the Higgs does not turn up at the Fermi lab, the $4 billion CERN machine may be able to find it starting in 2005. But that date seems a long way off for CERN physicists who see a possible discovery at hand.