Animated particle tracks showing the production and decay of a lambda particle. A negative kaon (yellow) enters from left, collides with a proton in the liquid hydrogen filling the bubble chamber, and produces a positive and a negative pion (orange and purple), and the lambda particle itself, which is neutral and therefore invisible. The lambda is revealed when it decays into a proton (red) and a muon (light blue). The muon soon decays into an electron (large green spiral) and an invisible neutrino. The positive pion (pink) knocks out an atomic electron, which forms the tighter of the green electron spirals. Tracks of particles not involved in the interaction are dark blue.