Animated particle tracks showing the production and decay of two W particles in the OPAL detector at the LEP at CERN, the particle physics laboratory near Geneva. This computer display shows OPAL in cross-section (green). An electron and positron annihilate at centre to produce two W particles. These live too briefly to be seen but reveal themselves by their decays. One W turns into a quark and an antiquark, which then produce two jets of particles (pale and dark blue tracks leading to yellow and magenta blocks). The other W decays to a muon (orange track, magenta block, red arrow) and an unseen muon neutrino. The positive and negative W particles are bosons, and are the carriers of the weak nuclear force, whose most visible manifestation is in radioactive beta decay.