Animated particle tracks of the production and decay of a lambda particle. A high-energy proton (yellow) enters from bottom, knocks out an atomic electron (green) in passing, then collides with a proton at rest in the liquid hydrogen of the bubble chamber. The collision produces seven negative pions (blue), nine positive particles (red), which include a proton and a kaon as well as seven positive pions, and the lambda. Being neutral the lambda leaves no track, but its existence is revealed when it decays into a proton (yellow) and a negative pion (purple). The lambda is one of the family of strange particles, which contain a strange quark.