Reports on Subfields of Physics: Elementary‐Particle Physics

In the past 20 years the subnuclear world—which, due to a seemingly endless supply of “elementary” particles, was once likened to a zoo—has become a gratifyingly orderly place. The Elementary‐Particle Physics Panel of the physics survey committee begins its report with a summary of the astounding progress of the last two decades: the emergence of a standard model of the universe as being made of quarks and leptons bound together by photons, gluons and W and Z particles; the unification of the weak and electromagnetic forces in a single gauge‐field theory; the understanding of baryon and meson structure in terms of quantum chromodynamics; the theory of interacting quarks and gluons; the possibility of a grand unification of all of the forces of nature; and the convergence of elementary‐particle physics and cosmology, each helping to elucidate the other. So much, the panel report explains, has been achieved. But many questions remain:

▸ What is the origin of mass, and what sets the masses of the different elementary particles? Is the Higgs hypothesis—which seeks to explain the breaking of symmetry—correct, and can the Higgs particles be found? If the Higgs hypothesis is wrong, what will replace it?

▸ Are there quark and lepton generations beyond the three already known? Why do these particles form generations?

▸ Are the quarks and leptons truly elementary, or does matter have a still deeper level of structure?

▸ Are new theoretical ideas like technicolor and supersymmetry correct? Can the strong and electroweak interactions be unified?

▸ Are there as yet undiscovered fundamental forces?