Homing in on the Higgs Boson

The mediators of the weak force—the W and Z bosons—are both roughly 100 times more massive than the proton, while the photon, which mediates the electromagnetic force, is massless. Based on symmetry principles, one would have expected the W , Z, and photon (collectively called gauge bosons) to all be massless. In order to generate the required symmetry breaking, one must invent a particular set of new particles and interactions, which ultimately provide an explanation of the origin of mass of the elementary particles. The simplest way to do this, and the one that is incorporated in the standard model of particle physics, predicts the existence of a particle called the Higgs boson [1]. The interactions of the Higgs boson with the quarks, leptons, and gauge bosons of the standard model are uniquely predicted by the theory, but the mass of the Higgs boson is a free parameter that can only be determined by experiment [2].