The Higgs Boson
All the known forces in the universe are manifestations of four fundamental forces, the strong, electromagnetic, weak, and gravitational forces. But why four? Why not just one master force? Those who joined the quest for a single unified master force declared that the first step toward unification had been achieved with the discovery of the discovery of the W and Z particles, the intermediate vector bosons, in 1983. This brought experimental verification of particles whose prediction had already contributed to the Nobel prize awarded to Weinberg, Salam, and Glashow in 1979. Combining the weak and electromagnetic forces into a unified "electroweak" force, these great advances in both theory and experiment provide encouragement for moving on to the next step, the "grand unification" necessary to include the strong interaction.
While electroweak unification was hailed as a great step forward, there remained a major conceptual problem. If the weak and electromagnetic forces are part of the same electroweak force, why is it that the exchange particle for the electromagnetic interaction, the photon, is massless while the W and Z have masses more than 80 times that of a proton! The electromagnetic and weak forces certainly do not look the same in the present low temperature universe, so there must have been some kind of spontaneous symmetry breaking as the hot universe cooled enough that particle energies dropped below 100 GeV. The theories attribute the symmetry-breaking to a field called the Higgs field, and it requires a new boson, the Higgs boson, to mediate it.
Searching for the Higgs boson is one of the high priority objectives of the Large Hadron Collider at CERN. At the end of 2011, the LHC results appear to limit the Higgs to between 114 and 145 GeV if it is to fit in the standard model of particle physics.
Fundamental force concepts