The End of the Frontier For Particle Physicists

The confirmation of the top quark was a triumph for particle physicists. But by filling in the final blank in the Standard Model's list of particles, they were left with little more to do. In a field that has been based on moving ever forward to new and deeper levels of understanding, coming to the end of the frontier was for particle physicists a frustrating situation.

The SSC, which would have accelerated two proton beams to energies of about 20 TeV, had been designed to break particle physics out of that impasse. For physicists who continued to dream of a few “ultimate” particles from which all others are made, the SSC provided the hope of finding evidence that both quarks and leptons are constructed of smaller, simpler parts. Aside from that quest, a primary mission of the SSC was to find one final piece of the Standard Model, a messenger particle called the Higgs boson that physicists think endows other particles with mass.

With the demise of the SSC, the search for the Higgs boson and for ultimate building blocks will most likely shift to Europe. The European Laboratory for Particle Physics (CERN) near Geneva, Switzerland, is planning to build a particle accelerator called the Large Hadron Colider (LHC), a proton-proton collider that initially will generate beam energies of about 5 TeV and may eventually reach 7 TeV. (Hadrons include any particles made of quarks.) For a while, it appeared that the LHC, too, might be axed, because several of the 19 CERN member nations were balking at paying for the expensive facility. But in January 1995, the project got the go-ahead.

For physicists who were gearing up to work at the SSC, the LHC was a decided comedown. It may not generate enough energy to produce significant numbers of Higgs particles, and in any event it will not be ready before the year 2003. Particle physicists say that, given such prospects, it is getting harder and harder to attract promising young people to the field. Other areas of physics, such as astrophysics and laser optics, appear to be “where the action is.” It is possible that after a highly productive 60-year reign on the forefront of physics, particle accelerators may finally be put to rest. Finding the top quark may prove to be one of their final triumphs.