The first observation of the decay of a kaon into 3 pions, recorded in special photographic emulsion by Cecil Powell's team at Bristol University in 1948. The kaon produces the dense track coming in from top right. It decays at A into 3 pions. One of the pions moves away slowly, leaving a dense track, & then interacts at B. The other 2 pions are faster & leave relatively faint tracks as they move off in opposite directions towards top right & bottom left. A & B is 25 micrometres). The kaon was the first discovered member of the family of "strange" particles, which contain a strange quark.
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