HIGGS PARTICLE

the carrier of an all-pervading fundamental field that is hypothesized as a means of endowing mass on elementary particles through its interactions with them. The field and the particle are named after Peter Higgs of the University of Edinburgh, one of the physicists who first postulated the idea. The Higgs field is different from other fundamental fields, such as the electromagnetic field, which underlie the basic forces between particles. First, it is a scalar field-i.e., it has magnitude but no direction. This implies that its carrier, the Higgs particle, has an intrinsic angular momentum, or spin, of zero, unlike the carriers of the force fields, which have spin. Second, the Higgs field has the unusual property that its energy is higher when the field is zero than when it is nonzero. The elementary particles therefore acquired their masses through interactions with a nonzero Higgs field only when the universe cooled and became less energetic in the aftermath of the big bang (the hypothetical primal explosion in which the universe originated). The variety of masses arises because different particles have different strengths of interaction with the Higgs field. The Higgs mechanism has a key role in the electroweak theory that unifies interactions via the weak and electromagnetic forces, as it explains why the carriers of the weak force, the W and Z particles, are heavy, while the carrier of the electromagnetic force, the photon, has a mass of zero. However, there is yet no experimental evidence for the Higgs particle, which would be a direct indication for the existence of the Higgs field. There is little theoretical guidance as to the mass of the particle, except that it should not be much more than 1 TeV (teraelectron volt). It is also possible that there may be more than one type of Higgs particle. Experiments are therefore being designed to search for Higgs particles in proton collisions at energies of 10 to 20 TeV. Christine Sutton